Summary of Invention
The present invention relates to a process for preparation of a-hexylcinnamaldehyde catalysed by a soft solid base catalyst, hydrotalcite and more particularly this invention relates to catalysed cross aldol condensation between benzaldehyde and 1-octanal to produce a-hexylcinnamaldehyde.

a-hexylcinnamaldehyde finds its applications extensively in perfumes, including soaps, for its floral and jasmine character, and in flavour compositions for its sweet and fruity notes. Also it is used in pharmaceuticals, organic synthesis and rubber raw materials.

Aldol condensation of benzaldehyde and 1-octanal is a reaction for synthesis of a-hexylcinnamaldehyde in which a strong liquid base sodium hydroxide or potassium hydroxide is used as a catalyst, quantitatively being more than in stoichiometric amounts and the reaction is carried out under homogeneous conditions applying temperature higher than room temperature say above 60 ?C under solvent and solvent free conditions. The reaction produces both the desired product, a-hexylcinnamaldehyde, via cross aldol condensation of benzaldehyde and 1-octanal, and the product of self-aldol condensation of 1-octanal, hexyldecenal. This homogeneous catalytic process includes lack of reusability of the catalyst. The use of hazardous liquid alkali, its tedious handling, storing and post-reaction treatment of spent liquid base, on one hand has a great environmental concern and on other hand lacks the cost effectiveness of the process. The cost effectiveness of this process significantly depends on handling of pre- and post-reaction treatment of the liquid base. With the trends towards developing environment friendly, cleaner technologies and minimizing the use of hazardous chemicals for the synthesis of a-hexylcinnamaldehyde, efforts are made to replace liquid base catalyst with solid base catalyst, thereby to make the process heterogeneous and avoid the use of harsh liquid bases. The hydrotalcite a solid base and layered double hydroxide exhibits unique properties as a catalyst as well as a support for a catalyst, to perform as a heterogeneous catalyst or to heterogenise a homogeneous catalyst. Also hydrotalcite as solid base is a potential alternate environment friendly material for substitution of liquid base like NaOH / KOH being practiced in the process of aldol condensation reaction.
Background of the Invention
Very few investigations for the synthesis of a-hexylcinnamaldehyde can be found in the literature. Reference may be made to L. S. Payne et al. in US Patent No. 5, 055, 621, 08 Oct. 1991, which reports the use of alkali, NaOH or KOH as catalyst for the aldol condensation of benzaldehyde and 1-octanal for synthesis of a-hexylcinnamaldehyde. The process involves the use of water for preparing alkali solution and glycol as a solvent for benzaldehyde and 1-octanal. The products obtained are cross aldol condensation product, a-hexylcinnamaldehyde, self-aldol condensation product, hexyldecenal and benzyl alcohol. The main drawbacks of this process are the use of hazardous liquid base KOH or NaOH which has major concerns for environment, cost, safety, handling, storage, disposal problems and post reaction work-up of these liquid bases. High capital expenses are also connected with the handling of liquid bases, KOH or NaOH. The formation of by-product benzyl alcohol is undesirable.

A. K. Sittard et al. in US Patent No. 5,728,892 17, March 1998, reports the synthesis of a-hexyl cinnamaldehyde by cross aldol condensation of benzaldehyde and 1-octanal using the liquid base, pyrrolidine as catalyst under solvent free conditions. This process involved use of acid during the reaction. The acids used were weak as well as strong like acetic acid, octanoic acid, p–toluenesulphonic acid, sulphuric acid and hydrochloric acid. The use of acid has afforded to enhance the selectivity of the desired product a-hexyl cinnamaldehyde. The acids used were more than 0.05 milliequivalent per gram of alkanal, 1-octanal. The major drawback of this process is use of liquid base as catalyst under homogeneous conditions associated with the concern of the separation of the catalyst. The use of acids particularly strong acids like sulphuric acid and hydrochloric acid are corrosive, and handling is difficult.

C. G. Kokotos et al. in their paper on “Microwave-assisted organocatalytic cross-aldol condensation of aldehydes”, RSC Advances (29, Jan. 2013, pp 4496-4499) reported a pyrrolidine catalyst for the cross aldol condensation of benzaldehyde and 1-octanal for the synthesis of a-hexylcinnamaldehyde using microwave irradiation under both solvent and solvent free conditions. The drawbacks of the process are the use of microwave which is not much viable cost effectively for the process at larger scale and the system is homogeneous which has the concern of the separation of the catalyst and its effective reusability.
Objective of the Invention
The main object of the present invention is to provide a heterogeneous catalytic process for preparation of a-hexylcinnamaldehyde which obviates the drawbacks as detailed above.
Another object of the present invention is to develop a process for preparation of industrially important fine perfumery chemical, a-hexylcinnamaldehyde.
Still another object of the present invention is to develop an environment friendly, elegant and cleaner method for synthesis of a-hexylcinnamaldehyde.
Yet another object of the present invention is to develop a solid base catalyst instead of liquid base catalyst being used for synthesis of a-hexylcinnamaldehyde.
Still another object of the present invention is to use a layered double hydroxide as a solid base catalyst.
Yet another object of the present invention is to use heterogeneous catalytic system.
Still another object of the present invention is to develop heterogeneous catalyst of effective reusability and recyclability.
Yet another object of the present invention is to avoid the use of solvent.
Still another object of the present invention is to prepare a-hexylcinnamaldehyde by a heterogeneous catalytic route which is ecologically and economically valuable.

Description of the Invention
Accordingly the present invention provides a heterogeneous catalytic process for the preparation of a-hexylcinnamaldehyde by aldol condensation of benzaldehyde and 1-octanal at temperature 30-200 ?Celcius which comprises (i) charging of the hydrotalcite catalyst of 3.5 Mg/Al molar ratio in the range of the amount of 2-200 mg into an oven dried double neck round bottom flask fitting one neck of the flask with refluxing condenser with spiral tube inside and blocking the other neck by a silicon rubber septum; (ii) circulating water at 15 ?Celcius in the spiral tube of the condenser and keeping the flask in an oil bath equipped with temperature controller and magnetic stirring unit; (iii) carrying out the reaction under nitrogen atmosphere for inhibiting the formation of corresponding acids from aldehydes; (iv) charging the flask with benzaldehyde in the range of molar ratio of benzaldehyde:1-octanal, 1:1 to 25:1 and tetradecane as an internal standard; (v) adjusting the temperature of the flask in the range of 30-200 ?Celcius; (vi) adding 1-octanal in the range of molar ratio of benzaldehyde:1-octanal, 1:1 to 25:1 to the flask through the second neck of the flask and stirring at 700 rpm for 8h; (vii) elegantly separating, reusing and effectively recycling the catalyst.
In an embodiment of the invention the catalyst may be heterogeneous, which is hydrotalcite with Mg/Al molar ratio selected in the range of 1.5 - 4.0 with characteristic layered double hydroxide.
In another embodiment of the invention, the catalyst hydrotalcite may be charged in the selected range of 2-200 mg.
In yet another embodiment of the invention, benzaldehyde and 1-octanal may be substrates in the molar ratio selected in the range of benzaldehyde: 1-octanal, 1:1 to 25:1.
In still another embodiment of the invention the temperature of the reaction mixture may be selected in the range from 30 to 200 ?Celsius.
In yet another embodiment of the invention the catalyst may be elegantly separated.
In still another embodiment of the invention the separated catalyst can be reused.
In yet another embodiment of the invention the catalyst may be effectively recycled in the selected range of 4-8 cycles.
According to the present invention the aldol condensation of benzaldehyde and 1-octanal was carried out using a solid base hydrotalcite, as catalyst. The reaction was carried out in a two neck round bottom flask with provision for attaching it with a spiral condenser with one neck and nitrogen inlet from another neck. In practicing this invention, firstly the catalyst hydrotalcite was charged in the range of 2-200 mg, wherein the molar ratio of Mg/Al was maintained in the range of 1.5 - 4.0. The substrate benzaldehyde was then added in the flask and the temperature was raised by maintaining in the range of 30-200 ?Celcius by keeping the flask in temperature controlled oil bath. After attaining the desired temperature the other substrate 1-octanal was added to the flask. The molar ratio of benzaldehyde to 1-octanal was maintained in the range of 1:1 to 25:1. The reaction was stirred at 700 rpm using magnetic stirring unit equipped with temperature controller and this time was considered as beginning of the reaction. The reaction was allowed to continue for 8h and the obtained product mixture was cooled to room temperature. The catalyst hydrotalcite was separated from this crude mixture. After separation of the catalyst, the yellow coloured mixture of the products was subjected to GC analysis. The products formed were a-hexylcinnamaldehyde in the range of selectivity of 30.0-85.0% and hexyldecenal in the range of respective selectivity of 70.0-15.0%. The separated fresh catalyst was washed, dried and reused for its recyclability.
In a typical experiment, hydrotalcite catalyst was added to a two neck round bottom flask. The neck of the flask was fitted with refluxing condenser with spiral tube inside and other neck was blocked using a silicon rubber septum. Water at 15oC was circulated in the spiral tube of the condenser and the flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The reaction was carried out under nitrogen atmosphere. The flask was then charged with 17-20 mmol benzaldehyde and tetradecane as internal standard. The temperature of the flask was adjusted at 125oC. Then 1-20 mmol of 1-octanal was added to the flask through the second neck of the flask and stirred at 700 revolutions per minute (rpm). After 8 h of the completion of reaction, the product mixture was cooled down to room temperature and the catalyst was separated by simple filtration by using Whatmann filter paper No. 42. After separation of the catalyst, the yellow color solution of the product mixture was then subjected to GC analysis. Analysis showed the formation of two neat products, (i) the cross aldol condensation product, a-hexylcinnamaldehyde in the range of selectivity of 30.0-85.0% and (ii) the product of self-condensation of 1-octanal, hexyldecenal in the range of selectivity of 70.0-15.0%. The separated fresh catalyst was then washed with methanol thrice and dried in a hot air oven at 80 ?Celcius. This dried catalyst was then reused for aldol condensation of benzaldehyde and 1-octanal under identical employed reaction conditions and it was considered the first recycling of the catalyst. The catalyst after first recycling was again separated, washed with methanol thrice and dried in a hot air oven at 80 ?Celcius, as mentioned above and reused for six times. The conversion and selectivity of the products remained almost identical up to six recycling.
In the present invention the aldol condensation of benzaldehyde and 1-octanal had been conducted in heterogeneous catalytic conditions in which the desired product a-hexylcinnamaldehyde was obtained with 81% selectivity and >98% conversion of 1-octanal. A hydrotalcite based solid base catalyst was found to be an efficient heterogeneous catalyst for aldol condensation of benzaldehyde and 1-octanal. This aldol condensation process involves some inventive steps viz (i) novelty resides in the catalyst’s function for the process of aldol condensation of benzaldehyde and 1-octanal to a-hexylcinnamaldehyde in which hydrotalcite catalyst effectively catalyzes this reaction affording 81% selectivity for the desired cross aldol condensation product, a-hexylcinnamaldehyde, (ii) the process works with solid base catalyst which obviates the need of usage and handling of hazardous liquid alkali like NaOH or KOH, (iii) the environmentally friendly solid base catalyst hydrotalcite is used and the process becomes non-hazardous, (iv) the process works under heterogeneous conditions which obviates the concern of separation of the catalyst against its homogeneous counterpart, (v) no solvent is used thereby avoiding the use of any organic solvent or the mixture of organic-water solvent, (vi) the avoidance of disposal problem by use of solid base hydrotalcite catalyst, (vii) the elegant separation and reusability of the catalyst, (viii) the capability of the catalyst for its effective recycling. The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention.

Example 1
For the synthesis of Mg-Al hydrotalcite solid base catalyst, an aqueous solution (0.2 L) containing nitrate salts of magnesium (0.223 mol) and aluminium (0.064 mol) for a ratio of Mg/Al=3.5, was added slowly to second (0.2 L) solution containing sodium hydroxide (0.72 mol) and sodium carbonate (0.21 mol) in 1 L round bottom flask under vigorous stirring. The addition took 3 h. The content was then transferred into the teflon coated stainless steel autoclave and aged at 70?C for 14 h under autogenous pressure. After 14 h, the precipitate formed was filtered and washed thoroughly with hot distilled water until pH of the filtrate was 7. The washed precipitate was dried in an oven at 80?C for 14 h. The Water used in all synthetic procedures was double distilled and deionized water. The XRD pattern of the as synthesized Mg-Al hydrotalcite depicted the characteristic of pure crystalline hydrotalcite showing sharp and intense peaks at lower diffraction angles (2? = 10-25?) with broad asymmetric reflections (2? = 30-50?) at the higher diffraction angles. The FT-IR spectra of the hydrotalcite showed the shoulders at 1647 and 1435 cm-1 for characteristic bands of H2O and CO32-, respectively. A band at about 541 cm-1 corresponded to the translation modes of hydroxyl groups, influenced by Al3+ cations. The peak was appeared at 664 cm-1 corresponding to the in-plane carbonate bending.
Example 2
A 75 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125oC. Then 3.93 mmol of 1-octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 2 h of the reaction, the product mixture was cooled down in the flask to room temperature. The yellow color solution of the product mixture was obtained and was analysed by GC. A conversion in terms of 1-octanal was 55.0% with 60.0% selectivity towards a-hexylcinnamaldehyde and 40.0% selectivity towards hexyldecenal.
Example 3
A 75 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125oC. Then 3.93 mmol of 1-octanal was added to the flask through the second neck of the flask and stirred at 700 revolutions per minute (rpm). After 4 h of the reaction, the product mixture was cooled down in the flask to room temperature. The yellow color solution of the product mixture was obtained and was analysed by GC. A conversion in terms of 1-octanal was 76.0% with 73.2% selectivity towards a-hexylcinnamaldehyde and 26.8% selectivity towards hexyldecenal.
Example 4
A 75 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125oC. Then 19.63 mmol of octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture is then subjected to GC analysis. A conversion in terms of 1-octanal was 94.0% with 34.0% selectivity towards a-hexylcinnamaldehyde and 66.0% selectivity towards hexyldecenal.

Example 5
A 75 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125oC. Then 9.81 mmol of octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture is then subjected to GC analysis. A conversion in terms of 1-octanal was 96.0% with 55.5% selectivity towards a-hexylcinnamaldehyde and 44.5% selectivity towards hexyldecenal.
Example 6
A 75 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125oC. Then 6.54 mmol of octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture is then subjected to GC analysis. A conversion in terms of 1-octanal was 97.0% with 66.0% selectivity towards a-hexylcinnamaldehyde and 34.0% selectivity towards hexyldecenal.
Example 7
A 75 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125oC. Then 4.91 mmol of octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture is then subjected to GC analysis. A conversion in terms of 1-octanal was 97.0% with 70.2% selectivity towards a-hexylcinnamaldehyde and 29.8% selectivity towards hexyldecenal.
Example 8
A 75 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125oC. Then 2.80 mmol of octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture is then subjected to GC analysis. A conversion in terms of 1-octanal was 98.0% with 79.6% selectivity towards a-hexylcinnamaldehyde and 20.4% selectivity towards hexyldecenal.
Example 9
A 75 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125oC. Then 1.96 mmol of octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture is then subjected to GC analysis. A conversion in terms of 1-octanal was 98.0% with 80.9% selectivity towards a-hexylcinnamaldehyde and 19.1% selectivity towards hexyldecenal.
Example 10
A 75 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 60oC. Then 3.93 mmol of octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture is then subjected to GC analysis. A conversion in terms of 1-octanal was 40.0% with 60.0% selectivity towards a-hexylcinnamaldehyde and 40.0% selectivity towards hexyldecenal.
Example 11
A 75 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 80oC. Then 3.93 mmol of octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture is then subjected to GC analysis. A conversion in terms of 1-octanal was 55.0% with 72.1% selectivity towards a-hexylcinnamaldehyde and 27.9% selectivity towards hexyldecenal.
Example 12
A 75 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 100oC. Then 3.93 mmol of octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture is then subjected to GC analysis. A conversion in terms of 1-octanal was 90.0% with 74.2% selectivity towards a-hexylcinnamaldehyde and 25.8% selectivity towards hexyldecenal.
Example 13
A 75 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 140oC. Then 3.93 mmol of octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture is then subjected to GC analysis. A conversion in terms of 1-octanal was 98.0% with 74.9% selectivity towards a-hexylcinnamaldehyde and 25.1% selectivity towards hexyldecenal.
Example 14
A 10 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125?C. Then 3.93 mmol of 1- octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture was then subjected to GC analysis. A conversion in terms of 1-octanal was 97.0% with 70.0% selectivity towards a-hexylcinnamaldehyde and 30.0% selectivity towards hexyldecenal.
Example 15
A 25 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125?C. Then 3.93 mmol of 1- octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture was then subjected to GC analysis. A conversion in terms of 1-octanal was 97.0% with 72.6% selectivity towards a-hexylcinnamaldehyde and 27.4% selectivity towards hexyldecenal.
Example 16
A 50 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125?C. Then 3.93 mmol of 1- octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture was then subjected to GC analysis. A conversion in terms of 1-octanal was 98.0% with 73.2% selectivity towards a-hexylcinnamaldehyde and 26.8% selectivity towards hexyldecenal.
Example 17
A 75 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125?C. Then 3.93 mmol of 1- octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture was then subjected to GC analysis. A conversion in terms of 1-octanal was 98.0% with 74.6% selectivity towards a-hexylcinnamaldehyde and 25.4% selectivity towards hexyldecenal.

Example 18
A 100 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125?C. Then 3.93 mmol of 1- octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture was then subjected to GC analysis. A conversion in terms of 1-octanal was 98.0% with 73.0% selectivity towards a-hexylcinnamaldehyde and 27.0% selectivity towards hexyldecenal.
Example 19
A 150 mg of the catalyst, hydrotalcite containing magnesium and aluminium in the molar ratio of 3.5:1 was charged into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and this catalyst charged flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. Then the temperature of the flask was adjusted at 125?C. Then 3.93 mmol of 1- octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture was then subjected to GC analysis. A conversion in terms of 1-octanal was 98.0% with 72.9% selectivity towards a-hexylcinnamaldehyde and 27.1% selectivity towards hexyldecenal.
Example 20
The experiment was conducted to study the recycling capability of the hydrotalcite catalyst and for that the hydrotalcite catalyst from the example 17 was separated with whatmann filter paper no. 42, washed trice with methanol, dried and the obtained amount of the catalyst was charged by employing identical conditions of example 17, into an oven dried double neck round bottom flask under nitrogen atmosphere maintained through one neck of the flask. Water at 15oC was circulated in the spiral tube of the condenser and the flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. The temperature of the flask was adjusted at 125oC. Then 3.93 mmol of octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture is then subjected to GC analysis. A conversion in terms of 1-octanal was 98% with 80.0% selectivity towards a-hexylcinnamaldehyde and 20.0% selectivity towards hexyldecenal with this recycled catalyst used for the first time.
Example 21
The hydrotalcite catalyst from the example 20 was separated with whatmann filter paper no. 42, dried and was charged into a oven dried double neck round bottom flask. One neck of the flask was fitted with refluxing condenser with spiral tube inside and other neck was blocked using a silicon rubber septum. Water at 15oC was circulated in the spiral tube of the condenser and the flask was kept in an oil bath equipped with temperature controller and magnetic stirring unit. The reaction was carried out under nitrogen atmosphere to inhibit formation of corresponding acids from aldehydes. The flask was then charged with 19.63 mmol benzaldehyde and 0.01 g tetradecane as internal standard. The temperature of the flask was adjusted at 125oC. Then 3.93 mmol of octanal was added to the flask through the second neck of the flask and stirred at 700 rpm. After 8 h of the completion of reaction, the product mixture was cooled down to room temperature. The yellow color solution of the product mixture is then subjected to GC analysis. A conversion in terms of 1-octanal was 98% with 79.0% selectivity towards a-hexylcinnamaldehyde and 21.0% selectivity towards hexyldecenal with this recycled catalyst used for the second time.
Example 22
The hydrotalcite catalyst from the example 21 was consecutively separated by the techniques mentioned in the examples 20 and 21 and reused for four more times under the identical conditions of examples 20 and 21. The yellow color solution of the product mixture is then subjected to GC analysis. A conversion in terms of 1-octanal with selectivity towards a-hexylcinnamaldehyde and hexyldecenal are given in the following table.
Cycle % Conversion % selectivity
a-hexylcinnamaldehyde hexyldecenal
Fresh 98 80 20
First 98 79 21
Second 97 78 22
Third 97 77 23
Fourth 96 78 22
Fifth 95 76 24

The main advantages of present invention are:
1. Unlike the catalytic processes described in the literature which either require strong liquid bases like NaOH/KOH or liquid base like pyrrolidine along with acids like acetic acid, octanoic acid, p–toluenesulphonic acid, sulphuric acid and hydrochloric acid as catalyst systems, present process uses solid base hydrotalcite as catalyst.
2. Substitution of eco-friendly solid base hydrotalcite in place of hazardous liquid bases like KOH and/or NaOH for aldol condensation.
3. Reduction of high capital costs involved in the handling of liquid bases like KOH and/or NaOH for this process.
4. Reduction of effluent problem in disposal of hazardous liquid bases like KOH and/or NaOH after aldolization reaction.
5. Unlike the reported processes, which are homogeneous, the present invention utilizes heterogeneous catalyst.
6. Unlike the reported processes, where liquid bases as catalyst are used in more than stoichiometric amounts, in the present invention the hydrotalcite is used in little catalytic amounts.
7. Unlike the reported processes, the handling of the solid base catalyst is safe and elegant.
8. Unlike the reported processes, the catalyst of present invention is easily separated, recycled and reused.
9. The present process can be easily adopted in the existing processes without major change for the synthesis of a-hexylcinnamaldehyde and that to, by minimizing the unit operation and storing the container for liquid base.

We Claim:
1. A process for the synthesis of a-hexylcinnamaldehyde by aldol condensation of benzaldehyde and 1-octanal using solid base heterogeneous catalyst comprising the steps: (i) charging hydrotalcite catalyst of 1.5 - 4.0 Mg/Al molar ratio into an oven dried double neck round bottom flask; (ii) circulating water at 15 ?C in the spiral tube of the condenser and keeping the flask in an oil bath; (iii) charging the flask with benzaldehyde and heated up in the temperature range of 30-200°C; (iv) charging 1-octanal into the warm benzaldehyde with continuous stirring at 700 rpm for 8h wherein the ratio of benzaldehyde and 1-octanal is maintained in the range of 1:1 to 25:1; (v) separating, reusing and effectively recycling the catalyst.
2. A process as claimed in claim 1, wherein the solid base catalyst is hydrotalcite in which the ratio of magnesium to aluminium is selected preferably in 7:2 ratio.
3. A process as claimed in claim 1, wherein the amount of the employed catalyst is in the range of 2-200 mg.
4. A process as claimed in claim 1, wherein benzaldehyde and 1-octanal are selected in the range of 19.63:19.63 mmol to 490.00:19.63 mmol.
5. A process as claimed in claim 1, wherein the reactions are carried out under solvent-free conditions.
6. A process as claimed in claim 1, wherein the catalyst used can be recycled.
7. A process as claimed in claim 1, wherein the recycled catalyst can be reused for 4-8 cycles.
Abstract
HETEROGENEOUS CATALYTIC PROCESS FOR SYNTHESIS OF ALPHA-HEXYLCINNAMALDEHYDE

This invention is an improved process for catalytic aldol condensation of benzaldehyde and 1-octanal for selective synthesis of industrially important perfumery chemical a-hexylcinnamaldehyde using a solid base hydrotalcite as heterogeneous catalysts replaceable with the existing harsh liquid homogeneous bases NaOH and/or KOH being practiced as catalyst for this reaction, in more than stoichiometric amounts. In this process, firstly catalyst is charged under nitrogen atmosphere into a typical two neck round bottom flask equipped with condenser for water circulation at required temperature followed by charging of benzaldehyde and 1-octanal in the desired molar ratio. The desired temperature of the flask kept in oil bath was raised and the agitation speed was maintained at 700 rpm and the reaction was allowed for desired time and the products obtained were analyzed by GC. The elegantly separated catalyst was reused and showed effective recycling.

Dated this-----------------------day of----------------------2016

Scientist
Innovation Protection Unit
Council of Scientific and Industrial Research

,CLAIMS:We Claim:
1. A process for the synthesis of a-hexylcinnamaldehyde by aldol condensation of benzaldehyde and 1-octanal using solid base heterogeneous catalyst comprising the steps: (i) charging hydrotalcite catalyst of 1.5 - 4.0 Mg/Al molar ratio into an oven dried double neck round bottom flask; (ii) circulating water at 15 ?C in the spiral tube of the condenser and keeping the flask in an oil bath; (iii) charging the flask with benzaldehyde and heated up in the temperature range of 30-200°C; (iv) charging 1-octanal into the warm benzaldehyde with continuous stirring at 700 rpm for 8h wherein the ratio of benzaldehyde and 1-octanal is maintained in the range of 1:1 to 25:1; (v) separating, reusing and effectively recycling the catalyst.
2. A process as claimed in claim 1, wherein the solid base catalyst is hydrotalcite in which the ratio of magnesium to aluminium is selected preferably in 7:2 ratio.
3. A process as claimed in claim 1, wherein the amount of the employed catalyst is in the range of 2-200 mg.
4. A process as claimed in claim 1, wherein benzaldehyde and 1-octanal are selected in the range of 19.63:19.63 mmol to 490.00:19.63 mmol.
5. A process as claimed in claim 1, wherein the reactions are carried out under solvent-free conditions.
6. A process as claimed in claim 1, wherein the catalyst used can be recycled.
7. A process as claimed in claim 1, wherein the recycled catalyst can be reused for 4-8 cycles.