Patented Nov. 7, 1950 2,529,186 UNITED STATES PATENT OFFICE PREPARATION OF CINNAMALDEHYDE Henry H. Richmond, Guelph, Ontario, Canada, assignor to United States Rubber Company, New York, N.Y., a corporation of New Jersey No Drawing. Application April 5, 1947, Serial No. 739,661 3 Claims. (CI. 260-599) 2 . This invention relates to the preparation of staying in the pink range of phenolphthalein in cinnamaldehyde by the alkaline catalyzed con dicator. The pH of the reaction mixture tends densation of acetaldehyde and benzaldehyde ac to fall due to the formation of benzoic acid from Cording to the equation. - the benzaldehyde. At the end of the reaction 5 the mixture is Slightly acidified to remove the CBO CH-CHEo -- H2O alkali and then is made slightly basic by the ad - CH3CHO - dition of Sodium bicarbonate. In practice it has been found easier to acidify and then make faintly alkaline with sodium bicarbonate than It has been found that a high yield (i. e., on () to reach the same pH by addition of acid; this the order of 75-85%, based on the benzaldehyde) procedure removes any benzoic acid present. of cinnamaldehyde can be obtained by adding The unreacted benzaldehyde can be recovered the acetaldehyde gradually to the benzaldehyde. by fractional distillation and in the same A reversal in the order of addition, or the simul fractionation, cinnamaldehyde is obtained in a taneous mixing, of the reagentS results in low State of high purity leaving behind high boiling yields, i. e., on the order of 18, and 49%, respec by-products. - tively. The duration of the period of time in which Preferably, the reaction is carried out at a the acetaldehyde is added to the reaction mix moderately elevated temperature Such as 70 C., ture materially affects the yield of cinnamalde although this reaction temperature may be 20 hyde obtained. For the batch size and efficient varied from 60-80° C. without too substantial a stirring, as set forth in Example. 1, the preferred loss in yield. As usual in this condensation a di addition time is 90 minutes, although this addi lute alkali catalyst is used, Such as Sodium hy tion time may be varied from 1 hour to 2 hours droxide, potassium hydroxide, lithium hydroxide, without too substantial a loss in yield. When trimethyl benzyl ammonium hydroxide, etc. 25 the addition time is lowered from 90 minutes to The addition of the acetaldehyde to the benz 20 minutes the yield falls from 81% to 72%. aldehyde avoids having present at any time an When the addition time is increased from 90 excess of acetaldehyde and thereby minimizes minutes to 3 hours the yield falls from 81% to the self-condensation of the acetaldehyde as Well 68%. as the further condensation of cinnamaldehyde 30 The duration of the period of time subsequent With acetaldehyde. to the addition of the acetaldehyde, and during By condensing a molecular proportion of the Which the reaction mixture is stirred while main acetaldehyde with a slight excess over a molecu taining the temperature at 70°C., materially af lar proportion of the benzaldehyde, there is fects the yield of the cinnamaldehyde obtained. maintained throughout, an excess of benzalde 35 For the batch size and efficient stirring described hyde which tends to prevent to some extent the in Example 1, the preferred duration of the pe formation of high boiling products which may be riod of time subsequent to the addition of the . formed in part if the acetaldehyde were in excess acetaldehyde and during which the reaction mix to condense With formed cinnamaldehyde as ture is stirred while maintaining the tempera aforesaid. 40 ture at 70° C., is 90 minutes, although this pe The acetaldehyde used in this process may be riod of time may be varied from 30 minutes to 3 added as a liquid or a gas or in aqueous solution. hours without too substantial a loss in yield. Further, it is not necessary that the benzaldehyde When this period of time is increased to 4 hours be highly purified. Technical grades of benz the yield falls from 81% to 70%. aldehyde containing Small amounts of chlorine 45 The ratio of the total weight of the aqueous may be used, since the chlorine containing in alkali medium to the weight of benzaldehyde and purities are removed in the final fractionation of acetaldehyde that are condensed, affects the the cinnamaldehyde. The quality of the cin yield obtained and the reaction time, since this namic aldehyde obtained is very good, analyzing factor in addition to the concentration of the as high as 99% pure and is suitable for the prepa 50 alkali in the aqueous medium regulates the ratio ration of flavors and perfumes. of benzaldehyde and acetaldehyde to the hy The pH of the reaction mixture should be droxyl ion present which acts as catalyst. The maintained by the addition of alkali from time preferred ratio of the weight of aqueous alkali to time in the region of 8 to 12, and especially medium to the weight of benzaldehyde and acet-- from 8.3 to 10. This is conveniently done by 55 aldehyde is 5:1, although the ratio may be varied 3,529, 186 3 4. from 6.5:1 to 2.5:1 without too substantial a loSS analysis the cinnamaldehyde is found to be 99% in yield. Decreasing the reaction volume in pure. - creases the productivity of the equipment used. While I have shown and described various emi The high boiling by-product which is recovered bodiments of the invention, it is to be understood after the removal of the unreacted benzaldehyde that the invention is susceptible to other modi and the cinnamaldehyde is a pleasant Snelling fications which appear within the spirit of the oil. Which is suitable as a masking odorant for invention and the scope of the appended claims. Such industrial products as rubber. Having thus described my invention, what I The following example is given to illustrate the claim and desire to protect by Letters Patent is: 10 1. A method for preparing cinnamaldehyde invention. which consists in heating a mixture of benzalde Eacample hyde and aqueous alkali solution of a concentra To a 2000 cc. three-necked fiask equipped with tion of from 0.23 to 0.6% by Weight at a tempera a, thermometer, a reflux condenser, a stirrer, and ture of from 60 to 80° C. while gradually adding a calibrated addition burette, jacketed so that it thereto acetaldehyde over a period of time of can be cooled by tap water, and whose tip is in from one hour to two hours, the amount of benz serted below the surface of the reaction mixture, aldehyde exceeding that molecularly equivalent there is introduced 150 g. of technical benzalde to the total acetaldehyde employed, thereafter hyde and a solution of 3.0 g. of Sodium hydrox heating the resulting mixture at the same temper ide in from 500 to 1300, preferably about 1000 cc. 20 ature for a period of time of from thirty minutes of water. The temperature of the mixture is to three hours, agitating the mixture throughout raised, with stirring, to 70° C. The temperature said heating steps, maintaining the pH of the re '70° C. is about the optimum temperature for high action mixture at from 8.0 to 12 throughout said yields concurrent with the other conditions de heating steps, maintaining a molecular excess of scribed in this example but the reaction can be 2: 5 benzaldehyde over acetaldehyde in the reaction carried out in the range 60-80° C. Maintaining mixture throughout said heating steps, and re this temperature, 48 grams of acetaldehyde is in covering cinnamaldehyde from the resulting re troduced through the addition burette, uniformly action mixture. over a period of 1%. hours. This constitutes the 2. The method of claim.1 wherein said cinnam period for one-half of the reaction. The alkalin aldehyde is recovered from the reaction mixture ity of the reaction mixture is periodically checked and from any benzoic acid present therein by and adjusted so that it is pink to phenolphthalein acidifying the reaction mixture, neutralizing the indicator by the addition of small quantities of acidified mixture with an excess of sodium bi sodium hydroxide Solution. This acidification is carbonate and thereby neutralizing any benzoic due to the oxidation of benzaldehyde to benzoic acid present, and separately recovering cinnama acid. The optimum alkalinity is that indicated aldehyde and the unreacted benzaldehyde from by the pink color of the phenolphthalein indica the resulting mixture by a method including fract tor. The stirring is continued for another hour tional distillation. - and a half at the same temperature. 3. The process of claim wherein each of said *: The reaction mixture is then acidified to pH 4 40 periods of time is substantially 90 minutes, where with 10% aqueous sulfuric acid solution, and al in the weight ratio of aqueous alkali medium to lowed to cool to room temperature; the excess Sul benzaldehyde plus acetaldehyde is substantially furic acid and any benzoic acid present is neu 5:1 and wherein said temperature is substan tralized. With an excess of sodium bicarbonate tially 70° C. . . . bringing the pH to 8. The slightly alkaline mix 45 . HENRY H. RICHMOND. ture is extracted with a water insoluble Organic solvent (200 cc. of benzene) and the whole is sub REFERENCES CITED sequently. poured into a Separatory funnel. The The following references are of record in the organic layer is separated; most of the solvent file of this patent: . . . . and all the water is removed by atmospheric flash 50 : distillation, and the residue consisting of benzal UNITED STATES PATENTS dehyde, cinnamaldehyde, and high boiling by Number Name 58,053 . Ach - Apr. 2U, 891 products,The products fractionated are: 63.9 in vacuo.g. benzaldehyde boiling. . . 1,716,822. Knorr et al. ------June 11, 1929 at 63? C. and 15 mm. n=1.546; 86.9 g. cinnamal 55 dehyde boiling at 123° C. and 15 mm. n=1.622, FOREIGN PATENTs and a higher boiling residue of 25 g. This repre Number Country. . . . . Date. sents a yield of 81% and a conversion of 46%. By 163,097 Japa