FORM 2
THE PATENT ACT 1970
(39 of 1970)
AND
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. Title of the invention:
"A METHOD OF PURIFYING CAPROIC ACID"
2. Applicant (s):
(a) Name: Godrej Consumer Products Limited
(b) Nationality: Indian company incorporated under the Indian Companies
Act, 1956
(c) Address: Pirojshanagar, Eastern Express Highway, Vikroli (East),
Mumbai - 400079, Maharashtra, India.
3. Preamble to the description
The following specification particularly describes the invention and the manner in which it is to be performed.


Technical field:
The present invention relates to a method of purifying Caproic acid, comprising the sequential steps of chlorination and fractional distillation, so as to separate the ketonic impurity from the crude Caproic acid.
Background and prior art:
Caproic acid, also known as Hexanoic acid, is the carboxylic acid derived from hexane with the general formula C5H11COOH. The salts and esters of this acid are known as hexanoates or caproates. Caproic acid is used in organic synthesis, manufacture of perfume, lubricants & greases, plastics, latex & rubber and dye, food additives and pharmaceuticals.
The commercial fatty acid materials typicaJly are discolored, and have a characteristic unpleasant rancid odors which are caused by the presence of volatile oxygenated organic compounds such as ketones and aldehydes. Malodorous carbonyl compounds which are contained in technical grade fatty acid sources are illustrated by methyl heptyl ketone, methyl nonyl ketone, butanal, heptanal, nonanal, deca-2-enaI, deca-2,4-dienal, and the like.
Various methods of deodorizing fatty acid materials are described in U.S. Pat. Nos. 2,265,020; 2,715,642; 2,795,453; 3,052,701; 3,124,460; 3,471,536; 3,526,649; 3,895,042; 4,294,821; and 4,938,957. The methods generally involve contacting a bulk fatty acid material with an adsorbent such as activated bentonite, or extracting the fatty acid material with a solvent such as furfural.
US5849348 describes a process for preparing a deodorized fatty acid salt feed supplement, wherein primary amine reagent is added to a process medium, in which C14 -C22 fatty acid with a content of malodorous carbonyl compound to obtain a deodorized C14 -C22 fatty acid alkaline earth metal salt product.
There is a continuing interest in the development of improved methods for deodorizing commercial fatty acid materials which have been selected for incorporation into animal feedstocks.
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US5215768 describe a method of deodorizing the Calcium Salt of C14-18 Fatty Acids, obtained from Palm Fatty Acid Distillate. The odour has been attributed to aldehydes and ketones in general and have been employed a chemical treatment with sodium bisulfite to neutralize malodorous aldehydes and ketones.
Though there are numerous patents on refining, purification, decolorization and deodorization of fatty acids, but none other than our earlier patent, IN 207074 has mentioned Nonyl Methyl Ketone as a specific impurity that needs to be eliminated in order to prepare a high purity fatty acid. Besides a method to eliminate Nonyl Methyl Ketone, IN 207074 has also described, in greater detail, the processes of distillation, fractional distillation of the composition of fatty acids in Coconut and Palm Kernel and the other non-fatty acid impurities in them.
IN 207074 (Application No. 239/MUM/2000) identified the major impurity in Caprylic acid, as Nonyl Methyl Ketone, and a method to eliminate it along with Caproic acid. Thus, due to the presence of Nonyl Methyl Ketone, fractions of crude Caproic acid were treated as a waste product. Literature is abundant with reports related to the genesis of Nonyl Methyl Ketone or 2-Undecanone, generated by enzymatic degradation of Laurie acid, the major fatty acid in Coconut, Palm Kernel and other "Laurie Rich" Oils. "Laurie Rich" Oils are also abundant in Caproic, Caprylic and Capric acids. Hence, in order to purify Caproic, Caprylic and Capric acids, there must be a process to effectively eliminate 2-Undecanone, which is always present in the fatty acid fraction containing a mixture of Caproic, Caprylic and Capric acids. IN 207074 describes a method of preliminarily purifying Caprylic acid prior to being distilled. The process involved the separation of Nonyl Methyl Ketone from the Caprylic acid by fractional distillation, but simultaneously also removing Caproic acid, since their boiling points are very close. However, the objective of the present invention, is to be able to separate Caproic acid from 2-Undecanone, and thus generate better value for the Caproic acid. As described in greater detail in IN 207074, the boiling points of Caproic acid and 2-Undecanone are not more than 3 to 4 degrees centigrade apart. This would make physical separation, even with the most efficient fractional distillation column, very difficult as well as partial. Hence, the only way to separate the two would be by chemical derivatization, since both of them have different functional groups - Ketone and Carboxylic Acid.
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The present invention thus differs from the aforesaid prior arts as the present invention relates to a method of combining the steps of chlorinating and distilling Caproic acid and more particularly to a method of preliminarily purifying Caproic acid prior to being distilled.
The chlorination of ketones at the alpha position has classically involved acid or light to initiate the substitution reaction of chlorine to ketones. These conditions can be some what limited in scope for several reasons, for example, they are also the conditions used to halogenate olefins. Alternative methods like Copper (II) Chloride have also been used to prepare alpha chloro-ketones. Other reported methods include the use of Trichloroisocyanuric acid, N-Chlorosuccinimide, Sulfuryl Chloride and P-Toluene Sulfonyl Chloride. According to usual practice, an unsymmetrical ketone is halogenated directly; yet, despite the choice of halogenating reagents; the kinetic and/or thermodynamic controls, low yields and/or difficult to separate mixtures are commonly expected
Since process of the present invention is not set out to isolate the mixture of chloro undecanone, and hence do not require the need for any of the above mentioned expensive reagents for chlorination. Thus the present invention involves the use of direct chlorination techniques mentioned in GB 489,552. This patent describes a method of preparing poly-halogenated ketones from mono-halogenated ketones, using simple stirring equipment and a facility to pass Chlorine gas. The current process is set out to prepare a mono or poly halogenated derivative of 2-Undecanone, the major impurity in crude Caproic Acid. Unlike the above mentioned patent, the current invention does not aim to isolate the mixture of chloro Undecanones, but instead is only a means of separating 2-Undecanone from Caproic Acid. By derivatization, the Boiling Point of the Caproic Acid will become much lower than the mixture of chloro Undecanones, and thus a means of separation has been achieved.
Another patent by the same inventors, GB 484,409 describes a process for specifically mono chlorinating or brominating ketones, however, the equipment required is a very elaborate counter current vapour phase equipment to perform this reaction. Once again,
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since the objective of the current invention is not the preparation of chlorinated ketone, it would be uneconomical to set up such elaborate equipment, just to remove a small amount of impurity from the bulk of the crude Caproic Acid. As explained in the above mentioned patent, the main drawback of the direct halogenation process is the effective removal of HC1. HO acts as a diluent and also causes molecular condensation of the ketone, thus slowing down the forward reaction. Other means of neutralizing the HC1 (Calcium Carbonate etc.) prove to be too cumbersome in the work-up and isolation of the mono chloro ketone. Thus the GB 484,409 has adopted the vapour phase reaction process, which obviates the need for a trapping medium to eliminate the HC1. However, the process described in GB 484,409 is also not economically viable on industrial scale as it involves high temperature and pressure throughout the reaction.
Thus the present invention aims to provide an efficient process for purification of Caproic acid, by combining the steps of chlorination followed by fractional distillation, thus separating the ketone impurity from the Caproic acid.
Objectives of the invention:
An object of the present invention is to achieve a more thorough and reliable separation of 2-Undecanone from Caproic acid.
Another object of the invention is to provide a simple chlorination method as compared to methods described in the prior art.
Summary of the invention:
In accordance with the above objectives, the present invention discloses a method of combining the steps of chlorination and fractional distillation, so as to separate the ketonic impurity from the Caproic acid. This invention discloses a method of initially chlorinating the ketonic impurity contained in the crude Caproic acid, followed by fractional distillation of the resultant mixture, so as to obtain purified Caproic acid.
Detailed description:
The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.
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As used herein the term 'crude Caproic acid' refers to crude caproic acid essentially consists of fatty acids of C6-C10 along with ketonic impurity, nonylmethyi ketone. Accordingly, the present invention describes a method of purifying Caproic acid, comprising the sequential steps of chlorination and fractional distillation, so as to separate the ketonic impurity from the crude Gaproic acid.
Thus chlorination is the preliminary step required to purify crude Caproic acid containing ketonic impurity. The principle behind the need for chlorination is the fact that the ketonic impurity, namely, 2-Undecanone or Nonyl Methyl Ketone (B.P. = 112 °C/15 mm), has a boiling point which is only 4 to 5 °C higher than Caproic acid (B.P. = 107 °C/15 mm). Thus, as mentioned in the background, physical separation, even with the most sophisticated and efficient fractionating column with the best of structured packing will not be effective. Hence the need to introduce a preliminary step of chemical separation, such as chlorination, which will form the chloro derivatives of 2-Undecanone, became imperative. The chloro derivatives of 2-Undecanone have much higher boiling points (even the Mono Chloro Undecanone has a B.P. = 137 - 140 "C/15 mm) than Caproic acid, and so the subsequent step of fractional distillation will easily and very effectively separate the two, thus producing purified Caproic acid. The present invention provides a process in which Caproic acid of natural origin is freed from undesirable ketonic impurities and separated from other fatty acids, if present, by combining the two steps of chlorination followed by fractional distillation, the product obtained being characterized by reproducible colour quality, high colour stability and by a better odour than the Caproic acid fractions obtained by known processes.
The improvements made in the present invention, include a simple process of chlorination, comprising a vessel fitted with an overhead stirrer, thermometer pocket, gas bubbler with a 2-way valve and an outlet for the residual gases. The vessel is held in water bath, maintained at 20°C all through the process. The appropriate amount of crude Caproic acid is taken in the vessel and kept stirring continuously, controlling the temperature of the reaction mass at 25°C. The acidic catalyst, p-toluene sulphonic acid is added to the reaction mass, and after 10 min., Chlorine gas is introduced into the reaction mass at such a rate that at no time should the temperature rise above 30°C. Further, the
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rate should also be such that the entire dose should be completed in about 3 hours. The total amount of Chlorine quantity to be dosed is calculated as under: (3 Moles of C12 / 1 Mole of 2-Undecanone) X Weight % of 2-Undecanone in crude Caproic Acid (as determined by GC)
At the initial stage, during the monochlorination, the HC1, generated as a by-product, hampers further reaction of C12 with the ketone, and preferentially the polychlorinated derivatives are formed. To ensure the complete and stepwise conversion of 2-Undecanone to Mono Chloro 2-Undecanone, it is preferred to drive out all the HCI as soon as it is generated.
This step is performed in the following manner:
After dosing CI2 for about 10 min., the 2-way valve is closed, and the entire reaction mass is flushed with N2 gas for 2 min. This will drive away all the HCI generated in the 10 min. of passing C12. This way, the chlorine is given enough time to react with the 2-Undecanone, but on the other hand, do not allow the HCI to accumulate in the reaction mass.
By doing this, the entire amount of C12 is dosed, passing C12 for 10 min. followed by N2 purge for 2 min., the entire exercise will take about 4.5 hrs.
At the end of the addition, the reaction mass is quenched with the appropriate amount of Bicarbonate, enough to neutralize the PTSA. The reaction mass is then washed free of alkali with water.
Analysis by GC indicates that the 2-Undecanone has been completely converted into mixture of monochloro and polychloro 2-Undecanone.
The mixture is now taken for fractional distillation between 65 - 110 °C at corresponding pressures of 0 - 15 mm of Hg to preferentially condense out the Caproic acid as a single fraction. This purified Caproic acid is now free of the 2-Undecanone, since the mixture of
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monochloro and polychloro 2-Undecanone have a boiling point which is > 30 °C above that of Caproic acid.
However, other procedures known to those skilled in the art or disclosed herein may be employed without departing from the spirit of the invention or the scope of the appended claims.
The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.
Example :
2 kg of crude Caproic acid, rich in Caproic acid (approx. 50%) having about 7 - 8 % of 2-Undecanone and the balance comprising Caprylic & Capric acids, was taken for processing in a 5 liter 4-necked flask, fitted with an overhead stirrer, thermometer pocket, gas bubbler with a 2-way valve and an outlet for the residual gases. The vessel was hold in water bath, maintained at 20 °C all through the process. One end of the 2-way valve was connected to a regulated supply of Chlorine (CI2) gas, and the other end was connected to a regulated supply of Nitrogen (N2) gas. The material was kept stirring all through the process, as well as controlling the temperature of the reaction mass at 25 °C. 10 gm of PTSA was added to the reaction mass, and after 10 min., C12 was introduced into the reaction mass at such a rate (hat at no time did the temperature rise above 30 °C. Further, the rate was also adjusted such that the entire dose should be completed in about
3 hours. The total amount of Chlorine quantity to be dosed is calculated as under:
(3 Moles of C12 / 1 Mole of 2-Undecanone) X Weight % of 2-Undecanone in crude Caproic Acid (as determined by GC) = 200.5 gm.
After dosing C12 for about 10 min., the 2-way valve was turned to allow N2 into the vessel and the entire reaction mass was flushed with N2 gas for 2 min. This will drive away all the Hydrochloric acid (HC1) generated in the 10 min. of passing C12. This way, chlorine is given enough time to react with the 2-Undecanone, but on the other hand, do
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not allow the HC1 to accumulate in the reaction mass. This step also enables the work up of the mass at the end of the reaction. Since there is negligible amount of HC1 in the reaction mass, the overall acidity is not very high, hence simple washings with water are enough to remove the acidity present due to PTSA and residual traces of HC1.
This way, the entire amount of CI2 was dosed, passing C12 for 10 min. followed by N2 purge for 2 min., the entire exercise taking about 4.5 hrs (3 hrs + 1.5 hrs).
At the end of the addition, the entire reaction mass was stirred for another 15 min., simultaneously purging with N2, to drive out most of the residual HC1. Nitrogen purge was stopped and under continuous stirring, almost the same amount of water (about 2 kg) was added to the reaction mass. Stirring was continued for about 15 min. and then stopped; allowed the reaction mass for about 30 min. for the layers to separate. The entire mixture was taken in a separator funnel and the clear water layer was drained out and checked for acidity. One more lot of water was taken and the entire exercise was repeated. This time the water layer that was drained out is no longer acidic. The reaction mass was dried under reduced pressure, to drive out all the residual moisture. The weight of the reaction mass is 2.103 kg.
Analysis of the reaction mass by GC indicates that the 2-Undecanone has been almost completely converted into a mixture of monochloro and.polychloro 2-Undecanones.

GLC Composition % Crude Caproic Acid (Before Chlorination) Crude Caproic Acid (After Chlorination)
Caproic C6 55.8 56.2
2-Undecanone 7.4 0.1
Caprylic C8 34.4 34.6
Capric C10 1.7 0.7
Mixture of Chloro 2-Undecanones Not Present 8.1
Other Non-Fatty Acid Impurities 0.7 0.3
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The total reaction mass (2.1 kg) was now taken in the standard equipment required for fractional distillation, i.e. a 3 liter 3-necked flask fitted with a thermometer pocket, a 1 meter fractionating column with structured packing, distillation head and a 1 liter receiver flask.
The temperature was gradually raised until there is a steady reflux at the head between 80 - 85 °C at 4 mm of Hg to preferentially fractionate out the Caproic acid as a single fraction. About 55% of the material is distilled out maintaining the above temperature and pressure. The distillate (1.110 kg.) comprises almost entirely Caproic acid, with some traces of Caprylic acid and other non-fatty acid impurities, but completely free of 2-Undecanone or its chlorinated derivatives, since the mixture of monochloro and polychloro 2-Undecanone have a minimum boiling point which is at least 25 °C above that of Caproic acid. The sample is analysed for AV, IV, SV, UM % and GLC composition. The purity of Caproic acid is > 98%, and its analysis is tabulated alongside that of the comparative example.
At 4 mm of Hg, the boiling points of all the components of crude Caproic acid, before and after chlorination, are tabulated as under:

Components in Crude Caproic acid B. P.° C at 4 mm pressure (Before Chlorination) B. P.° C at 4 mm pressure (After Chlorination)
Caproic Acid C 6 83 83
2-Undecanone 86 Not Present
Mixture of Chloro 2-Undecanones Not Present 108
Caprylic Acid C 8 110 110
Capric Acid C 10 133 133
Comparative Example:
2.1 kg of the same lot of crude Caproic acid, rich in Caproic acid (approx. 50%) having about 7 - 8 % of 2-Undecanone and the balance comprising Caprylic & Capric acids, was
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taken directly for fractional distillation, without carrying out the initial step of chlorination.
Following exactly the same conditions as described in the Inventive Example, the crude Caproic acid was taken in the standard equipment required for fractional distillation, i.e, a 3 liter 3-necked flask fitted with a thermometer pocket, a 1 meter fractionating column with structured packing, distillation head and a 1 liter receiver flask.
The temperature was gradually raised until there is a steady reflux at the head between 80 -85 °C at 4 mm of Hg to preferentially fractionate out the Caproic acid as a single fraction. About 55% of the material is distilled out maintaining the above temperature and pressure. The distillate (1.110 kg.) comprises of a mixture of Caproic acid, almost all the 2-Undecanone, some amount of Caprylic acid and traces of other non-fatty acid impurities. The sample was analysed for AV, IV, SV, UM % and GLC composition. The purity of Caproic acid was only about 85%, and its analysis is tabulated below, alongside that of the Inventive Example.

Distilled Caproic Acid (Comparative Example) Distilled Caproic Acid (Inventive Example)
Acid Value (AV) 410.9 471.1
Saponification Value (SV) 412.6 472.4
Iodine value (IV) I4.I 0.8
Unsaponiable Matter % (UM%) 12.8 0.5
GLC Composition %
Caproic C6 85.2 98.2
2-Undecanone 13.6 0.2
Caprylic C8 0.7 1.1
Other Non-Fatty Acid Impurities 0.5 0.5
Thus the Caproic acid obtained by the method of the invention, is > 98% pure and is essentially free of 2-Undecanone (about 0.2%). This would therefore be a good quality
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product to be used in premium goods. Further, most customers demand a Caproic acid having a purity > 98% and total non-fatty acid impurities < 1.0%.
In addition to the said examples, the following is the table showing the range of Boiling Points and their corresponding Pressures required to selectively remove the 2-Undecanone as its mixture of mono & poly chloro 2-Undecanones.

Component Pressure 2 mm Pressure 4 mm Pressure 7 mm Pressure
10 mm Pressure 15 mm
B. P. in ° C B. P. in ° C B. P. in ° C B. P. in ° C B. P. in ° C
Caproic Acid C6 72 83 94 99 107
2-Undecanone 76 86 97 103 112
Caprylic Acid C8 97 110 121 127 135
Mixture of Chloro 2-Undecanones 95 108 124 128 137
Capric Acid CIO 121 133 145 151 159
The preceding specific embodiments are illustrative of the practice of the invention. It is obvious, however, that other procedures known to those skilled in the art or disclosed herein may be employed without departing from the spirit of the invention or the scope of the appended claims.
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We Claim,
1. A method of purifying Caproic acid, comprising the sequential steps of chlorination of crude Caproic acid, to essentially separate 2-Undecanone, the major impurity, in crude Caproic acid, by Converting it into a mixture of Mono & Poly Chloro 2-Undecanones, and then fallowed by fractional distillation at temperatures ranging from 65 - 110 °C at their corresponding pressures of 0 -15 mm of Hg, so as to selectively distil out the purified Caproic acid, substantially free from 2-Undecanone.
2. The method as claimed in Claim 1, wherein said crude Caproic acid consists of fatty acids having 6-10 carbon atoms, along with 2-Undecanone as the major impurity.
3. The method as claimed in claim 1, wherein, the said method comprising a step of flushing the entire reaction mass with nitrogen to remove hydrogen chloride generated during the reaction.
4. The method as claimed in claim I, wherein the chlorination reaction is carried out at the temperature below 30°C.
5. The method as claimed in claim 1, wherein said chlorination reaction is carried out in presence of acidic catalyst, p-toluene sulphonic acid.
6. Pure caproic acid having a purity more than 98% prepared as per the process claimed in claims 1 to 5.
Dated this 30th day of September, 2008
Dr. Gopakumar G. Nair
Agent for the Applicant
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