2-METI4YL-3-(3,4-METHYLENEDIOXYPHENYL) PROPANAL, AND METHOD FOR PRODUCTION THEREOF TECHNICAL FIELD [0001] The present invention relates to 2-methyl-3-(3,4-methylenedioxyphenyl)propanal that is useful as a perfume (fragrance) and has a high purity, and a method for production thereof. BACKGROUND ART [0002] It is ordinarily known that odor characteristics of a perfume largely depend on a compound having an aroma and kinds of a slight amount of impurities contained therein or additives added separately. Changes of the formulation or composition of the substances may produce a novel aroma as a perfume or may produce an unpleasant smell. Therefore, the quality of the compound having an odor and the kind and compositional ratio of the minor component contained therein are substantially important for determining the value of the perfume product. Accordingly, a purification step is very important to obtain a perfume compound generating an aroma, on producing a perfume product. [0003] As a purification method of a perluHU' corapfiund, separation of irripur JtJ e.s by distill .i I ion m i ryoriHiiJ i.' separation, removal of impurities by ad.'ioi pt i on, clc. htive been known. However, special equipmc;nl:..y may be often required in the method other than distillation, and lor example, the adsorption method involves some problems, such as quality deterioration caused by elution of the adsorbent itself to the product. Otherwise, the purification by distillation can be easily carried out, but in the case where a target perfume compound is a high boiling point fraction, it is necessary to discard a large amount oi the jnil::id]. distillation fraction for preventing low boiling point impurities from being mixed therein, thereby providing a problem of decreasing the yield. Furthermore, under the heating condition, a prolonged period of distillation causes a decomposition of the perfume compound, and side reactions increasing impurities, and the impurities are mixed in the target product to finally provide a problem of deteriorating the quality and the aroma. [0004] 2-Methyl-3-(3, 4-methylenedioxyphenyl) propana.l is an ingredient of marine perfume that is widely used in an ordinary perfumery and cosmetics, such as perfume (eau.de cologne), soap, shampoo, conditioner, detergent, cosmetics, perfume spray, fragrance material, etc. (disclosed, for example, in Non-patent Document 1). As a method for producing 2-methy.l-3-(3, 4-me1:hylene-dioxyphenyl)propanal, such methods have been known as a method of carrying out finally hydrogenation reaction of 2-methyl-3-(3,4-methylenedioxyphenyl)-2-propenal via hieliotropin from obtained safrole purified from .'lasMri |-ras oil (disclosed, for example, in Patent PocmiiuMil 1), .i IIM'IIUHI MI produi;;ing from l-acetoxy-2-methyl-3- (3, 4- methylenedioxyphenyl)-1-propene (diyclosed, lor t-ix.-im|) In, in Patent Documents 2 and 3), and so on. Patenf Dooumeiifs 4 to 7 di.sclose a method of producing 2-ri\ethyl-3--(3, 4--int!f hy] ene~ dioxyfohenyl) propanal from 1, 2-methy] encMii.oxyhen/iMic as ,\ starting material. [0005] Patent Document 2 discloses that 1,2-methylenedioxy-benzene and 2-methyl-3,3-diacetoxypropene are reacted to synthesize l-acetoxy-2-methyl-3-(3,4-methylenedioxyphenyl)-1-propene, and then the compound is hydrolyzed to provide 2-methyl-3-(3,4-methylenedioxyphenyl)propanal as the target product. However, there is no description regarding to impurities and aroma, which are important for a perfume product, of the obtained 2-methyl-3-(3,4-methylenedioxy¬phenyl )propanal. [0006] [Non-patent Document 1] Angew. Chem. Int. Ed., vol.39(17), p.2980 (2000) [Patent Document IJ U.S. Patent No. 3,008, 9GB [Patent Document 2] JP-A-57-45124 [Patent Document 3] JP-A-2006-104151 [Patent Document 4] JP-A-55-141437 [Patent Document b] JP-A-2005-239619 [Patent Document 6] WO 2004/054997 [Patent Document 7] WO 2006/120639 DISCLOSURE OF THE INVENTION TECHNICAL PROBLEM [0007] The inventors have synthesized 2-methyl-3-(3,4-methylenedioxyphenyl)propanal according to the method disclosed in Patent Document 2, and also have synthesized i-acetoxy-2-methyl-3-(3,4-methylenedioxypheny1 ) -]-propene and then synl;hesized 2-metliY I -3- (3, 4-meUiy 1.«MUM Li oxyphcMiy I ) ■ propanal according to the method disclosed in Pa Lent Documents 4 and 7, but have confirmed that the compounds obtained by these methods did not have a sufficient aroma that is satisfactory as a perfume product. As a result of investigations on the factor deteriorating the aroma, .it has been found that by-produced acetic acid provides a problem. Although the formation process of the acetic acid is not clear, it has been confirmed that Reaction by-products, which are by-produced from l-acetoxy-2-methyl-3-(3, 4-methylenedioxyphenyl)-1-propene and the high boiling point compound in the subsequent step, are the major source of the acetic acid upon synthesis of l-acetoxy-2-mel:hyl-3-(3, 4-methylenedioxyphenyl)-1-propene . Furthermore, it has also been confirmed that a slight amount of 2-methyl-3-(3,4-methylenedioxyphenyl)propanal is decomposed to produce acetic acid. An object of the present invention is to provide 2-methy1-3-(3,4-methylenedioxyphenyl)propanal that has high purity enough to use as a perfume, and a method for efficiently producing the same. SOLUTION TO PROBLEM [0008] As a result of intensive investigations made by the inventors for solving the problems, it has been found that the problems on aroma are solved by controlling a concentration of less than 40 ppm of acetic acid in 2-methyl-3-(3,4-methylenedioxyphenyl)propanal. The present invention relates to a first invention [1] (production method) and a second invention [2] (substance), as shown below. [1] A method for producing 2-methyl-3-(3,4-methylenedioxyphenyl)propanal comprising: step (1): carrying out a process (A) inr ie,u-l.iiiq L,2-methylenedioxybenzene i:o|:)resented by the lo.l Lowi.luj loiiiiulii (1) with 2-methyl-3, 3-(,i i acetoxypropcMie Lepre.'jenI: t-'d by the following formula (2) or a process (B) tor icacl iinj I,,.''■■ methylenedioxyben'/.ene, methacrolein and acetic anhydr.i.de, thereby providing a reaction mixture containing l-acetoxy-2-methyl-3-(3,4-methylenedioxyphenyl)-1-propene represented by the following formula (3); [0009] (1) OCOCH3 OCOCH3 (2) (3) 'OCOCH3 [0010] step (2): providing a reaction mixture containing 2-methyl-3-(3,4-methylenedioxyphenyl)propanal represented by the following formula (4) by hydrolysis reaction or ester exchange reaction with an alcohol of subjecting l-acetoxy-2-methyl-3-(3,4-methylenedioxyphenyl)-1-propene represented by the formula (3) obtained in the step (1); and [0011] CHO K OCOCH3 (3) (4) [0012] Step (3): purifying by distillation of the reaction mixture obtained in the step (2), wherein the method further comprising at least one of the following procedures (a) to (d): Procedure (a): after the step (1), removing a compound having a boiling point higher than I-acetoxy ■ 2-iiu'l liy I • 3- (,i, 4--methylenedioxyphenyl)-1-propene from tlu' ii'actJun iiiixlurc containing the compound (formula (3)), t:heiuby ))rovidinq a crude product containing the compound (formula (3)); Procedure (b) : after the step (2), removing a (■.■ompound having a boiling point higher than 2-methYl"3-(-i, 4-methy Lenedioxyplienyl) propanal from the irs-iclion mixlure containing the compound (formula (4)), thertiby providing a crude product containing the compound (formula (4)); Procedure (c): carrying out purification by distillation in the step (3) at 210°C or less of a liquid temperature in a distillation vessel; and Procedure (d): after the step (3), carrying out washing, and neutralization or neutralization and adsorption. [2] 2-Methy1-3-(3,4-methylenedioxyphenyl)propanal having less than 40 ppm of acetic acid, which produced by the method according to the above [1]. ADVANTAGEOUS EFFECTS OF INVENTION [0013] According to the present invention, 2-methyl-3-(3,4-methylenedioxyphenyl) propanal that has high i.)urity eiioi.ic|h to use as a perfume, and a method for producing the same are provided efficiently. 2-Methyl-3-(3,4-methylenedioxy-phenyl)propanal obtained by the method of the present invention, for example, provides a more fresh and clear aroma as compared to the products obtained by the methods from safrole or heliotropin as starting materials disclosed in Patent Document 1, and thus has a new aroma that is distinguished from the conventional products. BEST MODE FOR CARRYING OUT THE INVENTION [0014] The method for producing 2-methyl-3-(3,4-methylene-dioxyphenyl)propanal of the present invention comprises the steps (1) to (3) and further comprises at li^ist i)(ii> nf i ii(> operations (a) to (d) . The steps {],) to (3) and the procedures (a) to (d) of the present invention will be described. [0015] Step (1) The step (1) is a step of carrying out a firocess (A) for reacting 1,2-methylenedioxybenzene represented by the following formula (1) with 2-methyl-3,3-diacetoxypropene represented by the following formula (2) or a process (B) for reacting 1,2-methylenedioxybenzene, methacrolein and acetic anhydride, thereby providing a reaction mixture containing 1-acetoxy-2-methyl-3-(3,4-methylenedioxyphenyl)-1-propene represented by the following formula (3). [0016] (1) OCOCH3 OCOCH3 (2) (3) '■H OCOCH3 [0017] [Process (A)] {Production of 2-Methyl-3,3-diacetoxypropene) The production method of 2-methyl-3,3-diacetoxypropene (formula (2)) used as a raw material of the process (A) is not particularly limited. For example, it can be produced by a process of reacting methacrolein with acetic anhydride in the presence of a catalyst (see JP-A-61-151152; "JP-A" means unexamined published Japanese patent publication) . The reaction process used in this invention, for example, includes a continuous .process, a semi-continuous process, a batch process and so on, and any of them may be employed. In the case of reacting methacrolein and acetic anhydride, a compound having Lewis acidity or a Rronsted acid may be used as a catalyst. [0018] Examples of the howls acidic c'ompound incLiuJfc' .1 haloqenated boron compound, such as boron i: t i f Inor.itic, boriMi trichloride, boroi\ tribromide, boron tr.liodJ de, I.H)I on trifluoride monoacetic acid complex, boron t rif luor i (Je diacetic acid complex, boron trifluoride diethyl ether complex, boron trifluoride tetrahydrofuran complex, boron trifluoride acetonitrile complex, boron trifluoride dihydrate., boron trifluoride n-butyl ether complex, boron trifluoride dimethyl ether complex, boron trifluoride methanol complex, boron trifluoride phenol complex, boron trifluoride phosphoric acid complex, etc.; a metal halido, such as aluminum fluoride, aluminum chloride, aluminum bromide, aluminum iodide, gallium fluoride, gallium chloride, gallium bromide, gallium iodide, indium fluoride, indium chloride, indium bromide, indium iodide, scandium chloride, scandium bromide, scandium iodide, yttrium chloride, yttrium bromide, yttrium iodide, titanium tetrachloride, titanium tetrabromide, titanium tetraiodide, zirconium tetrachloride, zirconium tetrabromide, zirconium tetraiodide, hafnium tetrachloride, hafnium tetrabromide, hafnium tetraiodide, iron trifluoride, iron trichloride, iron tribromide, iron triiodide, ruthenium trifluoride, ruthenium trichloride, ruthenium tribromide, ruthenium triiodide, zinc fluoride, zinc chloride, zinc bromide, zinc iodide, cadmium fluoride, cadmium chloride, cadmium bromide, cadmium iodide, mercury fluoride, mercury chloride, mercury bromide, tin fluoride, tin chlor.ide, tin bromide, tin iodide, antimony fluoride, antimony chloride, antimony bromide, antimony iodide, trihalide of a lanthanoid of an atomic number of from 57 to 71, etc.; copper triflate, copper trifluoroacetate, silver triflate, silver trif luoroacetate, zinc triflate, zinc tri L I i.ioroat'el tit e, cadmium triflate, cadiiiluin trifluoroac<;'i:,:il. c, I in itill.iii', tin trif luoroacetate, scandium triflate, sc: cata I y.Ml by adding an acid, a base or a salt, witliout wdl;er washing, and so on . [0021] [Process (B)] The process (B) is to react 1,2-methylenedioxybenzene, methacrolein and acetic anhydride. The procedure for the process (B) is not particularly limited, and synthesis of 1-acetoxy-2-methyl-3-(3,4-methylenedioxyphenyl)-1-propene may be carried out by the method disclosed in Patent Document 7, for example. The reaction process used in the production method includes a continuous process, a semi-continuous process, a batch process and so on, and any of them may be employed. The molar ratio of methacrolein and acetic anhydride is not particularly limited, and the ratio of acetic anhydride/methacrolein (molar ratio) is generally from 0.5 to 2.5, and preferably from 1.0 to 1.5. The molar ratio of methacrolein and 1,2-methylene¬dioxybenzene is not particularly limited, and the ratio of 1,2-methylenedioxybenzene/methacrolein (molar ratio) is generally from 0.5 to 50, preferably from 2 to 10, and more preferably from 3 to 6. In the case of reacting 1,2-methylenedioxybenzene (formula (1)), methacrolein and acetic anhydride, ihe compound having Lewis acidity or the Bronsted acid may be used as a catalyst. The amount of the catalyst used, the reaction temperature and the post-treatment after (.'.ompleting the reaction are the same as those in the product;! on conditions for l-acetoxy-2-methyl-3-(3,-1-methy lenedioxyphenyl) - I-propene described in the pi i H'O.IM (A). [0022] In the process (A) and the process (B) in l:,h(,> .s'Lep (1), after completing the leaction, the resu-ltiiig react.! on iiiixlure contains unreacted 1,2-methylenedioxybenzene (formula (1)) and a group of compounds having higher boiling point, than L-acetoxy-2-methyl-3- (3, 'l-methylene-di oxypheny I) -] -propene (which are hereinafter referred to as "high boiling point compounds A") in addition to l-acetoxy-2-methyl-3-(3,4-methylenedioxyphenyl)-1-propene (formula (3)) as the target product. These reaction mixtures can be purified by a conventional method, such as extraction, filtration, condensation, distillation, recrystallization, crystallization, column chromatography and so on, and in consideration of industrial manufactures, impurities are preferably removed by distillation or crystallization. The removal of the unreacted 1,2-methylenedioxybenzene may be carried out simultaneously with the removal of the hi.gh boiling point compounds A (procedure (a)), but is preferably carried out prior to the procedure (a). Di.st illtjt: i on (oi: removing the unreacted 1,2-methylenedioxybenzene from the resulting reaction mixture is generally carried out from 4 0 to 175°C (from 1 to 760 torr), and preferably from 50 to 150°C (from 3 to 300 torr), in consideration of the boiling points of 1,2-methylenedioxybenzene, (109°C at 80 torr) and 1-acetoxy-2-methyl-3- ( 3, ) ,icel y I >"'<''"n,ri c, etc.; an antimony compound, such as ani:.i,mony cai boxyiat-e (e.g., aiitiraony ar;etat,c) , antimony a.lkox.i dc;, etc.; a zirconium compound, sucli as zirconium alkoxiile (c.ij., zirconium propoxide, zirconium butoxlde), /. i ircoii iuiii ' acetylacetonate, etc.; a titanium compound, such a.'j t.i i: anJ uiti alkoxide (e.g., titanium tetraethoxide, titanium tetraisopropoxide, titanium tetrabutoxide), etc.; a tin compound (e.g., dibutyltin oxide, dibutyltin diacetate, dibutyltin dilaurate, tin oxide). The organic metal catalyst may be used solely or in combination of two or more kinds thereof. The amount of the catalyst for the ester exchange reaction depends on the kind of the catalyst, and is generally 1 mol or less, preferably from 0.001 to 0.5 mol, and more preferably from 0.005 to 0.3 mol, per mol of 1-acetoxy-2-methyl->3- ( 3, 4-methylenedioxyphenyl) -1-propene . [0037] The reaction may be carried out with an organic solvent optionally added for increasing the solubility of the catalyst. The organic solvent used in this invention may be appropriately determined depending on the kind of the catalyst used, and is not particularly limit:ed within performing increasing of the solubility of l.he catalyst and not disturbing the reaction. For example, the organic solvents include a ketone compound, such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, etc.; an aliphatic carboxylic acid, such as acetic acid, piopionic acid, butyric acid, etc.; an aliphatic carboxylate ester, such as methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, etc.; a halogen solvent, such as methylene chloride, chloroform, chlorobenzene, etc.; and a polar solvent, such as acetonitrile, tetrahydrofuirin, N,N-dimethylformamide, N, N-dimethylimidazolidiiione, N-methylpyrrolidone, dimethylsulfoxide:, liex.iiiifl:fiy I phoMphni i >■ triamide, etc. The solvent may be used soleJy or in combination of two or more kinds thereof. Tlie organic solvent may be recovered after comf).! t:;t, j nq fhe reaction, and then reused in next, ti.me. [003B] The temperature of the ester exchange reaction depends on the kind of the alcohol and the amount of the catalyst, and is generally from 0 to 150°C, preferably from 20 to 120°C, and more preferably from 30 to 100°C. In the case where l-acetoxy-2-methyl-3-(3,4-methylene-dioxyphenyl)-1-propene (formula (3)) remains in a large amount after completing the reaction of the step (2), the compound (formula (3)) is gradually decomposed in the step (3), which may generate acetic acid, and therefore, the conversion ratio of l-acetoxy-2-methyl-3-(3,4-methylene¬dioxyphenyl) -1-propene is preferably 90 wt% or more, more preferably 95 wt% or more, and further preferably 98 wt% or more. [0039] The reaction mixture in the step (2) contains I:he catalyst used, and it is preferred as a post-treatment that the catalyst is neutralized with an acid or a base, or the reaction mixture is washed with water, an acidic aqueous solution or a basic aqueous solution for removing the catalyst. Without performing neutralization or washing, water, an alcohol or the organic solvent, which used in the reactions, may be removed by distillation, or 2-methyl-3-(3,4-methyloncdioxyphenyl)propanal may be purified hy distillation. But in that case, the targeted 2-methyl-3-(3,4-methylenedioxyphenyl)propanal may be cause some problems by decomposing by the remaining catalyst. In the hydrolysis reaction, acetic acid is formed as a by-product, and the acetic acid can be effectively removed from the reaction mixture by washing wit.h l:he .'KI I ii t i on .IM ri post-treatment. [0040] (Removal of High }U,");i.l i mi Point Compound:,; H) In the case where the step (2) .is car:.) led onl williont carrying out the procedure (a) in the present invention, I h(^ alcohol, water, the acetate ester by-produced, and the organic solvent, which used in the reactions, are removed from the resulting reaction solution after completing the reaction, and then the procedure (b) is preferably carried out for removing a group of compounds as by-products having higher boiling point than 2-methyl-3-(3,4-mothylenedioxy-phenyl) propanal (boiling point: 158 °C' at 10 torr) (which are hereinafter referred to as "high boiling point compounds B"). The procedure (b) can prevent a generation of acetic acid from the high boiling point compounds B in the subsequent step (3). The high boiling point compounds B herein are a mixture of various compounds, for example, including unreacted 1-acetoxy-2-methyl-3- ( 3, 4-rtiethylenedioxyphenyi ) -1-propene, 1,2-bis (3-acetoxy-2-methyl-2-propenyl) -4 , 5-methylenodi,oxybenzene (formula (5)), impurities derived from these compounds, such as 1,2-bis(2-methyl-3-oxo-propyl)-4,5-methylenedioxybenzene (formula (6)) and 1-(3-acetoxy-2-methyl-2-propenyl)-2-(2-methyl-3-oxopropyl)-4,5-methylenedioxybenzene (formula (7)), compounds formed by decomposing these compounds, etc. In addition, compounds, such as polymers derived from methacrolein, 2-methyl-3,3-diacetoxypropene, l-acetoxy-2- p. b- methyl-3-(3,4-methylenedioxyphenyl)propane and 2~methyJ-3-(3, 4-methylenedioxyphenyl ) propanal, etc. arc also contained. [0041] 'ococi ^^^. 6HO OHC OHC (7) (6) [0042] As the proceduio (b) for removjnq 1:he liigh bo:i I. .i nf,| point, compounds B, conventional metlioils may l^e eiiipLoyed, such as extraction, filtration, condensation, d istillai: Lon, recrystallization, crystallization, column chromatography and so on, and a purification by distillation is most preferred. (Purification by Distillation) The process and the opportunity of the distillation purification, the kind of the rectification column, etc. are the same as those in the distillation purification described for the procedure (a). Since 2-methyl-3-(3,4-methylenedioxyphenyl)propanal (formula (4)) is liable to be decomposed thermally, the distillation purification is preferably carried out with a thin film evaporator, a falling liquid film evaporator, etc., which undergoes a short residence time. Charging for distillation and taking out fractions are preferably carried out under an inert gas. In the case of using a packed rectification ciolunm, the kind of the packing is not particularly limited. Since 2-methyl-3- (3, 4-methylenedioxyphenyl) propanaJ. is decomposed significantly, the distillation temperature is higher, and the yield is lower. It is preferred to use a structured packing in order to make the difference in pressure between the head part and the bottom part of the rectification column smaller, for preventing the liquid temperature of the distillation vessel from being set at a high temperature. The kind and the specification of the structured packing that can be used are the same as those described for the procedure (a) . While the disti.llation conditions on reracwinq the high boi-l.ing point compounds B are not par I. i cii I ti i, i I 1 iMt.i on by distillation of the reaction mixture containing 2-methyl- 3-( 3, 4-methylenedioxy|:)honyl) propana I obi ,:j LIKMI j n l.ln' .slop (2). (Puri f icat,i.on by \)x s I. i I I.ri tion) The process and tlie opportunity of the pur:i l;:i.cdl, i on by distillation, the kind of the rectification column, tlie kind of the packing in the step (3) are the same as those in the distillation purification described for the procedures (a) and (b) . Since 2-methyl-3-(3,4-methylenedioxyphenyl)propanal (formula (4)) is gradually decomposed thermally during distillation, a continuous process and a semi-continuous process, which undergoes a short residence I. Lme, arc preferred. The actual numbers of plates and the reflux ratio (refluxed amount/distilled amount) in the distillation purification in the step (3) are the same as those in the procedure (b) . A reflux ratio of less than 0.1 lowers the isolation efficiency, and an excessive reflux ratio is not preferred, since decomposition of l-methyl-3-(3,4-methylenedioxyphenyl)propanal and other reaction may be accelerated. [0044] (Procedure (c)) In the step (3), the purification by distillation is preferably carried out at 210°C or less of a liquid temperature in the distillation vessel of the distillation apparatus (procedure (c)). More specifically, the temperature :i a prefeifibly tiie range from 100 to 210°C, more preferably from 140 to 210°C, and further preferably from 150 to 200^0, at the lic!dd pdrl: of the rectification column, under reduced pressure (from 0.1 to 100 torr (from 0.013 to 13.332 kPa)). Upon rol h ■> •! ,i uq I lio finaJ. product (upon distilling the iiiriii) I i ,)cl.:.i du ) , I lii> J i quid temperature in the distillation vessel of Lhe di ML 1. I la l, 1 on apparatus is 210°C or Jess, preferably the range from 125 to 210°C, more preferably trom 130 to 200"C, further pieferably from 135 to 190°C, particularly preferably from .1-10 lo I8.'>"C, and most preferably from 145 to 180"C. The fem|,)i.'i a I uit' exceeding over 210"C i.s not preferred, since 2-iiiet.hy I.-3-(.3, 4-methylene-dioxyphenyl)propanal itself is decomposed to form acetic acid and then this acid may be mixed in the main fraction, even though the high boiling point by-product and impurities do not present in the solution in the distillation vessel. High vacuum is required, in the case of distilling with a lower liquid temperature in the distillation vessel. In this case, it is necessary to use a special vacuum pump with high performance and to use a rectification column with a larger size therefor, which is not economically advantageous. Accordingly, for providing 2-methyl-3-(3,4- methylenedioxyphenyl)propanal with high purity as the final product, it is preferred to carry out the purification by distillation under tho conditions of the proceduri' (c). Particularly, in the case where t:!)e rlj sti ) J.a l;:i on purification is carried out by a batch process, 2-methyl-3-(3, 4-rnethylGnedioxyphenyl) propanal is liabio to bo decomposed since the residence time thereof in the rectification column is prolonged, and the amount of acetic acid formed may be increased, as compared to the continuous rectification process. Accordingly, the distillation temperature is preferably the range from 130 to 210°C, and more preferably from 140 to 185°C, in the batch process. Charging for distillation and taking out fractions are preferably carried out under an inert gas. 2-Methy1-3-(3,4-methylenedioxyphenyl)propanal with high purity containing less than 40 ppm of acetic acid on t>t> obtained by the di.sti llation purification of the .step (3). [004.'j] (Procedure (d)) (Washing, Neutralization, or Neutralization and Adsorption) A crude product containing 2-inethyl-3-( 3, 4-mel:liy 1 f.-ne-dioxyphenyl) propanal liaving an acetic acid content of 4 0 ppm or more may also be obtained by the di.sti.ll ation jjuri fi cation of the step (3). Accordingly, the obtained crude product may be subjected to the procedure (d) of washing with water, washing and neutralization with an aqueous solution of a basic compound, or neutralization and adsorption. 2-Methyl- 3-(3,4-methylenedioxyphenyl)propanal, having an acetic acid decreased to less than 40 ppm, can be obtained as the l:inal product by the procedure (d). (Washing with Water, or Washing and Neutralization with Aqueous Solution of Basic Compound) The amount of water used for washing in the procedure (d) is not particularly limited, and is generally the range from 0.1 to 50 times, preferably from 0.2 to 10 times, more preferably from 0.3 to 5 times, and further preferably from 0.5 to 1.5 times, with respect to 1 g of 2-methyl-3-(3,-1-methylenedioxyphenyl) propanal obtained in Llie sLe|) (3). While the crude product may be washed only with water, the crude product may be washed with an aqueous solution oP a salt, such as sodium chloride, sodium sulfate, etc., in the case where it is difficult to separate into the organic phase and the aqueous phase. By washing with an aqueous solution of a basic compound, such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, etc., acetic acid is neutralized, and an acetic acid salt thus formed can be distributed to the aqueous phase, thereby decreasing the acetic acid content. The opportunity of washing is not particularly limited, and washing operations with water, an aqueous solution of a salt, and an aqueous aolution of a basJ.c ci:)nipounpa i: ..IIHI I wiioii the temperature is from 4(1 to 70°C. [0046] 2-Methy1-3-(3,4-methylenedioxyphenyl)propanal may contain water after washing with water or washing with an aqueous solution of a basic compound. Accordingly, the water may be removed if desired, for example, by distillation, drying under reduced pressure, or dehydration by drying agent. The method for removing water is preferably disl j.i Lation . The distillation condition is preferably a pressure of from 10 torr to ordinary pressure, but there is no particular limitation, in the case where the temperature is at 210°C or less. The residue in the distillation vessel after removing water may be the final product, or may be again subjected to distillation purification under the same conditions as in the procedure (c) in the step (3). [0047] (Neutralization, or Neutralization and Adsorption) By contacting with a basic compound or passing through a column filled by them, particularly a basic ion exchange resin, acetic acid in 2-methyl-3-(3,4-methylenedioxy¬phenyl) propanal obtained in the step (3) may be neutralized the containing acetic acid, or the resulting acetate salt removed by filtration or adsorption with the basic ion exchange resin. Thus the content of acetic acid can be decreased to less than 4 0 ppm. The operation is generally carried out from 0 to 80"C. [0048] According to the present invention, /'-iae1 hy l- 1-( i, 4-methylenedi oxyplienyl) pr. o|,)anal havinii Jo.s.', rli,.u'i 4(1 pi'in 'd acetic acid can be e:l:l ij::iently produciMl, and a i^u-'i. Limit,'i recognized that acetic acid contained in 2-iiii5thy 1-3--( 3, 4-methylenedioxyphenyl) pi.opanal in an aniounL ot: ie.vss l:haii 40 ppm (Joes not affect the aroma thereof. 2-Methyl-3- (3, 4-methylenedioxypheny I ) |)i:'opana L olMained by the production metJiod of the preserii: inv(»ntion fi.is an aroma that is different from 2-methyl-3-(3,4-methy1ene-dioxyphenyl)propanal produced from safrole or heliotropin. EXAMPLES [0049] The present invention will be described specifically with reference to examples and comparative examples. In the examples and comparative examples below, "%" means "% by weight" unless otherwise indicated. In the present invention, [1] the purity of 2-methyl-3-(3,4-methylenedioxyphenyl)propanal, [2] the acetic acid content, and [3] the reaction .yield after completing the step (2) and the distillation yield in the step (3) were-determined in the folJowi.ng manners. [0050] [1] Purity of 2-Methyl-3-(3, 4-methylenedioxypheny.l) propanai A high performance liquid chromatography (HPLC) apparatus "CLASS-VP" manufactured by Shimadzu Corporation (analytic column: "TSKgel ODS-80Ts, QA 4.6 mm x 250 mm" manufactured by Tosoh Corporation) was used, an eluant of acetonitrile/0.1% phosphoric acid aqueous solution = 40/60 (volume ratio) was used, and the apparatus was set at pH 2.5, a flow rate of 1.0 mL/min and a column oven temperature of 40°C. An UV detector was used, the measurement wavelength was 252 nm, and the sample injection amount was 20 |.iL. The sample for analysis was prepared by weighing 0.8 g of a sample to be measured to a 50-mT. volumotric (-|,isk, and then filling the flask by diluting wit:h arelon i tr i 1 c. 5 tiiL of L.lje 1 eaii Itlng /iolril, J ..n was coll fi.-lc'ii f-y i WIM-IC )'i|M>rii> and placed in a 50-mL volumetric fJask, and then it was filled by diluting with acetonitrile. The i.'(>sult.i.nq solnl ion was examined for analysis. [0051] [2] Acetic Acid Content A gas chromatography apparatus "GC-14B" manufactured by Shimadzu Corporation (detector: FID system; analytic column: TC-WAX (0.53 mm x 30 m, membrane thickness: 1.0 |.im) manufactured by GL Sciences, Inc.) was used, and the content of acetj.c acid was measured and calculated by the absolute calibration curve method. 0.6 ^.iL of 2-methyl-3-(3, 4-methylenedioxypheiiyJ ) piopanal as a target reference was injected by a l-|.iL microsyringe. The injection temperature was 220°C, the detector temperature was 260°C, and the column temperature was maintained at 80°C for 3 minutes, increased to 115°C at a rate of 5°C per minute, increased to 230°C at a rate of 40°C per minute, and then maintained at 230°C for 20 minutes. [0052] [3] The reaction yield {%) after completing the stej) (2) and the distillation yield (%) in the step (3) were calculated by the following equations. Reaction yield (%) after completing step (2) == [mole of 2-methyl-3-(3,4-methylenedioxyphenyl)propanal/mole of methacrolein, which used in the reaction] x 100 Distillation yield (%) in step (3) = [(weight of main fraction/molecular weight of 2-methyl-3-(3,4-methylene¬dioxyphenyl) propanal) /mole of 2-methyl-3-(3,4-methylene¬dioxyphenyl) propanal in charged solution] x 100 [0053] Example 1 (Production of 2-methyl-3-(3,4-methylenedioxy¬phenyl) propanal) [Step (1)] 1,703 g of acetic anhydride and 2.9 (| of boron trifluoride diethyl el.tior complex wni e placi'd undfM ,) nitrogen gas atmospheres in a 2 0-L separabh; l;lask i:'(.|u;i |)[)ed with a stirrer, a thei.monieter and a i:()nii(:)n;it'r. 1,021 (\ of methacrolein (purity: 96.1%) was added dro|)wLse Ihcjreto whiie maintaining the liquid temperature in the range fi:om 0 to 20°C. The mixture was stirred at the range from 9 to 11°C for 2 hours to provide a mixed solution containing 2-methyl-3,3-diacetoxypropene. 8,200 g of 1,2-methylenedioxybenzene was added to the mixed solution, to which 56.9 g of boron trifluoride diethyl ether complex was then gradually added dropwise, and the mixture was stirred at a J iquid temi:)erature of from 38 to 41°C for 4 hours. After completing the reaction, the resulting reaction mixture was washed with water, the organic phase was collected by separation and extraction, and unreacted 1,2-methylenedioxybenzene was recovered by distillation from the organic phase, thereby providing 3,380 g of a residue containing l-acetoxy-2-methyl-3-(3, 4-methylenedioxyphenyl)-1-propene. The composition of the residue was 02.8?. of 1-acetoxy-2-methyl-3-(3,4-methylenedioxyphenyl)-1-propene (formula (3)) and 8.6% of 1,2-bis(3-acetoxy-2-methyl-2-propenyl)-4 , 5-methylenedioxybenzene (formula (5)). [Step (2)] 3,044 g of methanol and 25.0 g of potassium carbonate were mixed with the residue, and the mixture was stirred from 30 to 50°C for 4 hours to carry out ester exchange reaction until the conversion ratio of l-acetoxy-2-methyl-3-(3,'1-methylenedioxyphenyl)-1-propene reached 99%. After completing the reaction, the resulting reacLion soLution was mixed with 23.6 g of a 75% phosphoric acid aqueous solution, followed by stirring. Methyl acetate anil methanol, piodih-t'd tlirdiigh Mic reaction were distilled off, and the result iiig conceiiLr ate was washed with water to provide 2,6'\h g ot a j:i;'acl.ion mixture of 2-methyl-3-- (3, 4-methylened:i oxyplitniy] ) pri)|.)dn>i,l . The resulting reaction mixture was analyzed t)y the aforementioned melihods. As the result, Ji had a purity oj 78.0-6 and contained about 20% of the higli boiljng point, compounds B. The reaction yield of 2-methyl-3-(3,4-methylenedioxyphenyl)propanal based on l-acetoxy-3-(3,4-mcthylenedioxyphenyl)propene was 88.8%, and the reaction yield of 2-methyl-3-(3,4-methylenedioxyphenyl)propanal based on methacrolein was 75.9%, by HPLC analysis. Subsequently, 834 g (net amount: 651 g) of 2,616 g of the reaction mixture was distilled with a rectification column (packing: Laboratory Packing EX, trade name, manufactured by Sulzer Chemtech, Ltd., diameter: 25 mm x height: 1,100 mm) with a 1-L flask equipped with a stirrer, a thermometer and a condenser, 32.6 g of an initial fraction was distilled off at a reflux ratio of 7, and then 596 q (net amount: 589 g, purity: 98.9%) of a crude product, which had been removed the high boi.ling point c()m|:50uiid.s D, wat; t)bl ained by the distillation under a pressure of 7 t.orr (0.'333 kPa), a temperature of the bottom part of from 177 to 210"C, a temperature of the head part of from 152 to 153°C and a reflux ratio of 1 [procedure (b)]. [Step (3)] The resulting crude product was again distilled with the rectification column with the 1-L flask equipped with the stirrer, the thermometer and the condenser. 110 g of an initial fraction was distilled off at a reflux ratio of 10, and then 450 g of 2-methyl-3-(3,4-methylenedioxyphenyl)-propanal as the final product obtained as the main fraction by the distillation under a pressure from 7 to 8 torr, a temperature of the bottom part from 170 to lOOT:, ,i temperature of the head y^art from 153 to I'l'l^C ami a nd lux ratio oJ: 1 [procedure (c) J . The resulting 2-methyl-3-(3,4-mothylenedioxyphenyl)-propanal had a purity of: 99.4%, the content of an acetic acid was 19 ppm and a distillation yield was 69.1'*. [0054] Upon collecting the main fraction, the distilled fraction was sampled by dividing into 10 fractions, and the fractions were evaluated by perfumers according to the following standard. The results are shown in Table 1. (Standard for Evaluation) o: The specimen had no acid smell in the aroma and was able to be used practically as a perfume. X: The specimen exhibited abnormal odor and was not be able to be used practically as a perfume. Moreover, the difference in aroma from a commercial product (available from Acros Organics) was also evaluated. The results are shown in Table 1. o: The specimen had an aroma that was different from the commercially available product. x: The specimen had the same aroma as the comnercidlly available product. -: The specimen was not evaluated. [0055] Table 1 Distilled fractions Initial fractio n 1 2 3 7 10 15 Total Fraction (g) 110 30 30 30 30 30 30 450 HLF purity (%) 94.59 98.89 99.04 99.13 99.38 99.56 99.75 99.39 19 Acetic acid content (ppm) 1,735 52 39 28 15 I _ o o 5_ o o Evaluatio n Evaluation in odor X X o o 0 o o Difference in aronna from commercially available product - - o o o Note: HLF [005( is an abbreviation o 5] f 2-methy l-3-(3,4-n nethylene dioxyphe nyl)prop< anal. According to Table 1, it is understood that a specimen having less than 40 ppm of acetic acid was dble i.o 1H> wnv.d as a perfume, since abnormal, odor was round in the IM.SC wlic-rc the acetic acid ctintenl was 40 ppm oi mort;. I''uii. he uuor<:', J L is understood that a specimen contaiiiJn(( N>.'is tliaii 40 (ipiii ol acetic acid was a new peirfume that exh Lb i.tcd a liosli c\\\i\ clear aroma that was different from the commercial. p.i;och.ict. However, the distilled fractions (2, 3, 7, 10 and W-'J) were not able to be distinguished from each other by slight difference in aroma owing to the difference in acetic acid content (from 5 to 39 ppm). [0057] Example 2 (Production of 2-methyl-3-(3, 4-methylenedi.oxy- phenyl)propanal) [Step (1)] 1,736.5 g of acetic anhydride and 4.1 g of boron trifluoride diethyl ether complex were mixed under a nitrogen gas atmosphere in a 20-L separable flask equipped with a stirrer, a thermometer and a condenser. 1,071 g of methacrolein (purity: 94.2%) was added dropwise thereto while maintaining the liquid temperature in the range from 0 to 20°C. The mixture was stirred for 2 hours to provide a mixed solution containing 2-methyl-3,3-diacetoxypropene. 8,200 g of 1,2-methylenedioxybenzene was added to tlie mixed soJ.ution, and then 61.7 g of boron trifluoride diethyl ether complex was gradually dropwised. After completing the dropwise addition, the mixture was stirred at a liqu.i.d temperature from 38 to 42°C for 4 hours. After completing the reaction, the resulting solution was washed with water, the organic phase was collected by separation and extraction, .nid unreacted 1,2-methylenedioxybenzene was distilled off. 3,589 g of the resulting solution was t:ransferred to a simple distillation apparatus and distilled (pressure: 3 torr, temperature: 1B2°C) to provide 3,058 g of a main I. faction as a crude product. In I.lie main fraction, the purl I y ol I acetoxy-2-methyl-3- (3, -l-methylenedioxypheny I.) -1-ptJ )perif was 94.4°,, and the purity oC 1, 2-bis (3-actitoxY-2-mel. hy 1.-2-propenyl)-4, 5-niethylenedioxybenzene ( fornuil.a (5)) wiis 1.3V, [procedure (a)]. [Step (2)] 3,235 g of methanol and 24.4 q of potassium (:;arbonate were mixed in a 10-L separable flask equipped with a stirrer, a thermometer and a condenser, to which the solution of 1-acetoxy-2-methyl-3-(3,4-methylenedioxyphenyl)-1-propene, which had been heated to the temperature from 78 to 82°C, was gradually dropwised with stirring at 30°C. After completing the dropwise addition, the mixture was stirred at 30 to 50°C for about 5 hours to carry out ester exchange reaction. The conversion ratio of l-acetoxy-2-methyl-3-(3,4-methylenedioxyphenyl)-1-propene after completing the reaction was 98.0%. 22.8 g of a 75% phosphoric acid aqueous solution was added to the reaction solution, followed by stirring, and then methanol and methyl acetate by-produced were disti].led off under reduced pressure. The resulting concentrate was washed with water to provide 2,424 g o (: a ciude piodi.iiM o.l. 2-methyl-3-( 3, 4-methylenedioxyphenyl) propanal (purity: 94.1'h) . The analysis of the resulting crude product .indicated that the reaction yield of 2-methyl-3-(3,4-methyleiie!dioxy-phenyl)propanal based on l-acetoxy-2-methyl-3-(3,4-methylenedioxyphenyl)-1-propene was 96.2%, and the reaction yield of 2-methyl-3-(3,4-methylenedioxyphenyl)propanal based on methacrolein was 82.4%. [Step (3)] Subsequently, 783 g (net amount: 737 g) of the crude product of 2-methyl-3-(3,4-methylenedioxyphenyl)propanal was distilled with a rectification column (packing: L,:iboratory Packing EX, trade name, manufactured by Sulzer Chemtech, Ltd., diameter: 2 5 mm x heJghl:: 1,100 mm) with /i I-Ti (Lrsk. \ iVi i\ of an initial fraction was distilled off ,it a M'I, lux t,ii. io of 10, and then 480 g of 2-methyl-3-(3,4- methylenedioxyphenyl) propanal (purity: 99.7%, acetic ac.ld content: 5 ppm) as the final product was collected as the main fraction at a pressure of from 6 to 7 ton, a liquid temperature of the d.ist.illation vessel of from 172 to 2()0°C, a temperature of the head part of from 14 8 to ir)l°C and a reflux ratio of 1 (distillation yield: 64.9%) [procedure (c)] . The aroma of the resulting 2-methyl-3-(3,4-methylene-dioxyphenyl)propanal contained no acid smell and was evaluated favorably by the perfumers. The distillation yield was 65.1%. [0058] Example 3 (Production of l-acetoxy-2-methyl-3-(3,4-methylenedioxyphenyl)propene by process (B)) 22.1 g (300 mmol) of methacrolein, 36.8 g (360 nimol) of acetic anhydride and 171.2 g (1,410 mmol) of 1,2-methylenedioxybenzene were placed and mixed in a 300-mL three-neck flask equipped with a stirring device and a thermometer. 0.97 g (6.0 mmol) of iron(IIT) chloride (anhydride) was gradually added thereto while malntn i ii:i ng l:he internal temperature to from 5 to 45"C', followed by stirring for 5 hours. After completing the reaction, 200 ml, of water was added to the resulting reaction product, followed by stirring for 10 minutes. Subsequently, after separating the aqueous phase, 200 mL of water was again added to the organic phase, followed by stirring for 10 minutes. The aqueous phase was again separated, and the resulting organic phase was analyzed by HPLC. As a result, the yield amount of 1-acetoxy-2-methyl-3-(3,4-methylenedioxyphenyl)-1-propene was 54.9 g (yield based on methacrolein: 78.1%). The amount of produced 1,2-bis(3-acetoxy-2-methyl-2-propenyl)-4 , 5-methylenedioxybenzene (formula (5)) was 7.2 g (yield: 7.1%). Thc-'.reaf te ir, tlie same opera ticjiiM .i;; I he pi (M i M In i (- (.1), the step (2) and the step (3) (procedu,i:(> (c)) in hlxdinp] i> ,'' were carried out to provide 27.7 g ni 2-meLhyl- ■!--( l,'\-methylenedioxyphenyl) propanal. The aiiiount: ol acdic /icicl contained in the result.i.ng 2-methyl-'i-{-i,'1--irK?thy I oned ioxy-phenyl)propanal was 18 ppm. [0059] Reference Example 1 (Step (2): Ester Exchange Reaction using Metallic Catalyst) After carrying out the same procedures as the step (1) and the procedure (a) in Example 2, 2.24 g (70.0 mmol) of methanol and 0.284 g (1.00 mmol) of titanium(IV) isopropoxide were mixed under a nitrogen gas atmosphere in a 25-mL three-neck flask equipped wil:h a stirrer, a thermometer and a condenser. 2.34 g (10.0 mmol) of l-acetoxy-2-methyl-3-(3,4-methylenedioxyphenyl)-1-propene was gradually dropwised thereto with stirring at 30 to 50°C. After completing the dropwise addition, the mixture was stirred at 30 to 50°C for about 1 hour. After completing the reaction, the resulting reaction solution was analyzed by HPLC. As a result, the conversion ratio of l-acetoxy-2-methyl-3-(3, 4-methylenedioxyphenyl)-1-propene was 100%, and the selectivity of 2-methyl-3-(3,4-methylenedioxyphenyl)propanal was 96%. In the step (2), 2-methyl-3-(3,4-methylenedioxy¬phenyl) propanal can be obtained with a high selectivity by ester exchange reaction using a metallic catalyst such as titanium(IV) isopropoxide . Thereafter, the step (3) and the procedures (c) and (d) in Example 2 may be carried out. [0060] Reference Example 2 1 mL of 2-methyl-3-(3, 4-methylenedioxy|,)henyl) propanai having an acetic acid content of 5 ppm (purity: 99.6'-;., having been confirmed that no high boiling point coinpcMiiid h wa.s contained) obtained J ri t.lie same maniu-'T a;; In Example :' wa;-. placed in a 2.5 mL-stainless steel ve^yael, and wa;'. .•i(;'a,led by plugging. Four of the vessels were placed in oil baths at prescribed temperatures (185°C, 200"(:, 220"i:' and 2 3(l"r:, respectively) and allowed to stand. AfMen lapsing a presc:ribed period of tiirio, the vessel.') were taken out ('roiii the oil bath, and the purity of 2-meLhyl-3-(3,'l-metliy lene-dioxyphenyl)propanal and the acetic acid content were measured. The results obtained are shown in Table 2. [0061] Table 2 Temperature Amount of compounds Elapsed time Oh 24 h 48 h 72 h 96 h 185"C HLF (wt%) 99.6 99.7 99 98.6 97,4 Acetic acid (ppm) 5 8 10 98,9 12 "~97.'8 ^32" 12 96.3 36 "93.1 ' 47 200''C HLF (wt%) 99.6 99.2 Acetic acid (ppm) 5 17 24 220°C HLF(wt%) 99.6 98.2 96.5 95.4 44 Acetic acid (ppm) 5 34 38 230°C HLF (wt%) 99.6 95.7 94 36 90.4 35 Acetic acid (ppm) 5 46 - Note: HLF is an abbreviation of 2-mettiyl-3-(3,4-methylenedioxyphenyl)propanal. [0062] According to Table 2, it is understood that 2-raethyl-3-(3,4-methylenedioxyphenyl)propanal is decomposed significantly and the amount of acetic acid formed is also increased, when the temperature upon distillation is 220°C or more . It is also understood that the temperature upon distillation is desirably 210°C or less, and preferably 200°C or less, in consideration of Table 1 that abnormal odor is observed when the acetic acid concentration is 4 0 ppm or more [0063] Reference Example 3 2-MeLhyl-3- (3, 4-iiiethylenedioxy[jheiiyl) |it:opriiid L w,:i;:i synthesized in the same manner as in Example 1, and t:he purification step is carried out in tlie same matuier to collect the main fraction. Thereafter, the liquid temperature in the distillation ves.sel was heated to 220"C, and then the rectification was finished after confirming l:hat no distillation occurred. 40.0 g of the residue after the distillation was the high boiling point compounds B containing 20.6% of 2-methyl-3-(3,4-methylenedioxyphenyl)-propanal and the residue contained a mixture of various kinds of polymers. The high boiling point compounds D were added to the 2-methyl-3-(3,4-methylenedioxyphenyl)propanal (purity: 99.6%) obtained by the distillation purification to adjust the content of the high boiling point compounds B to 7.4% and 16% The mixtures were examined for time-lapse change in, for example, amount of acetic acid at 185°C in the same manner as in Reference Example 2. The results are shown in Table 3. [0064] Table 3 Content of high boiling point compoiinds B 0 wt% Elapsed time Oh 24 h 99.7 48 h 99,0 " 72 h 98.6 96 h 97.4 Amount of HLF (wt%) 99.6 HLF residual ratio (%) 100 100 96.7 99.4 98.2 Amount of acetic acid (ppm) 5 8 10 12 12 7,4 wt% Amount of HLF (wt%) 92.6 90.7 88.6 85.6 82.4 HLF residual ratio (%) 100 98.0 95.7 92.4 89.5 Amount of acetic acid (ppm) 13 46 65 110 118 73.8 16 wt% Amount of HLF (wt%) 83.2 80.6 79.3 76,4 HLF residual ratio (%) 100 96.8 95.3 91.8 88.7 Amount of acetic acid (ppm) 26 95 178 196 244 Note: HLF is an abbreviation of 2-methyl-3-(3,4-methylenedioxyphenyl)propanal. [0065] According to Table 3, it is understood th.it it is more preffirred (diat the high boilJ.ng poini cmripi iiinds H .nc iciiiuvcd before providing the final product, .<;i.nce i'.-tnetliy I. • <■• {^, 4-methylenedioxyphenyl) propanal is deooiDposoil sign 1 (: i raiitJ y ai^d the amount of generated acetic acid is Jmrrf^ased in the cise where the content of the high boiling point: oompoinids B is increased. [0066] Comparative Example 1 (Example where the procedures (a) Lo (d) were not carried out) 722 g (net amount: 563 g) of 2,616 g of reaction mixture of 2-methyl-3-(3,4-methylenedioxyphenyl)propanal (purity: 78.0%), which had been obtained in the same manner as in Example 1 except that the procedure (b) in the step (2) was not carried out, was purified by distillation by using a rectification column (packing: Sulzer Laboratory Packing EX, trade name, manufactured by Sulzer Chemtech, Ltd., diameter: 25 mm x height: 1,100 mm) with a 1-L flask. A main fraction was obtained after the area percentage of the fraction in gas chromatography reached 99% or more. Upon collecting the initial fraction, the reflux ratio was 10, and the main fraction was distilled at a reflux ratio of 1. During distilling the main fraction, the pressure was from 7 to 8 torr (from 0.933 to 1.066 kPa), the liquid temperature in the distillation vessel was from 175 to 220°C, and the temperature of the head part of a rectification column was from 152 to 153°C. The initial fraction was 182 g, the ma.i.n fraction was 320 g, and the purity of 2-methyl-3-(3, 4-met:hylenedioxy-phenyl)propanal was 99.7%. The content of acetic acid was 104 ppm, and it was not able to be used as a perfume, because of the odor containing acid smell significantly. The distillation yield was 56.8%. It was understood from the results of Comparative Example 1 that even though the purity of 2-iiietliy I - 3-{ 3, 4-methylenedioxyphenyl) [ii opanal was I .n gel i,ii cidiul was 99.7">, it was not able to be used as rrs. After completing the reaction, 0.56 g of 85'^ phosphoric acid was added for neutralization, and then uintidcted methanol and by-produced methyl acetate were distilled off by simple distillation. 37.8 g of water v;as added to the residue after the simple distillation, followed by stirring at 40 to 50°C. The mixture was then placed in separating funnel, and 42.5 g of an organic phase was obtained. The content of 2-methyl-3- (3,4-methylenedioxyphenyl)propanal in the organic phase was analyzed by HPLC to calculate the reaction yield, wliich was 8 5.1?,. The same procedures as above were carried out by using mixtures that were changed in content (mol%) of l,2-bis(3-acetoxy-2-methyl-2-propenyl)-4,5-methylenedioxybenzene. The results obtained are shown in Table 4. [0069] In Reference Example 4, the influence of l,2-bis(3-acetoxy-2-methyl-2-propenyl)-4,5-methylenedioxybenzene (formula (5)), in the case where the procedure (a) in the step(l) were not carried out, was investigdlocl (JII the step (2) . As a result, it was found thai when I lie coiileni- of 1,2-bia ( 3-ac'etoxy-2 -niel:hy.l -2-propenyl) -■'I, 'i-iiU'l hy Leiin I i nxyl KM I:'.I MU' was 9.5 mol% or more, the yield of 2-iTiethy.l - i-(3, 4 methylenedioxyphenyl) propanal as the tartiel i:)rodu('i liecame 85% or less and the content of the high boiling |)o.i.nl'. compounds B tended to be increased. Tliese lead lo Llie demerit that the aroma of the produi:.t may ln' easy to be adversely affected and that the loss upon