Patented Dec. 12, 1939 2,183,325

v . UNITED s'ra’rss PATENT lr-FFwE 2,183,325 MANUFACTURE OE UNSATURATED ACID-S Hanns Peter Staudinger, Ewell, England, assign or to The Distillers Company Limited, Edin burgh, ‘Scotland, a British company No Drawing. Application December 6,1938, Se rial No. 244,289. In Great Britain January 1, 1938 5 Claims. (01. 260--530) The present invention relates to the oxidation vary within wide limits and mixtures of 80% of unsaturated aliphatic aldehydes to their cor or more by volume of crotonaldehyde with 20% responding acids and particulary but not exclu or less by volume of acetic acid can be oxidised sively to the production of crotonic acid from with good yields, In order to carry out the proc 5 crotonaldehyde. ess, air or oxygen may be blown through a mix The direct oxidation of unsaturated aldehydes ture of crotonaldehyde and per acetic acid but such as crotonaldehyde by means of air or oxygen an alternative method is to pass the mixture of gives poor yields is effected at ordinary or moder crotonaldehyde with per acetic acid downwards ate temperatures owing to productionof formic through a packed column in counter-current to a stream of air. > 10 acid, and when the temperature is raised by 10 products of a resinous or tarry nature are formed. The resultant crotonic acid can be recovered It is known to effect the conversion of acetalde by ?ltration or by simple distillation from the hyde into acetic acid by the oxidation of a weak acetic acid and any unchanged crotonaldehyde. solution of the aldehyde in acetic acid, but it is High yields of pure crotonic acid free from res inous or tarry products are obtained. 15 not practicable to carry out the oxidation of 15 crotonaldehyde in crotonic acid since this is a In place of crotonaldehyde other unsaturated solid at ordinary temperature-moreover the aldehydes may be oxidised to the corresponding presence of the crotonic acid does not inhibit acids e. g. methyl acrolein may be oxidised to entirely the tendency to form resinous or tarry methacrylic acid. 2o by-products when the temperature is raised. The following examples illustrate the manner 20 According to the present invention the oxida in which the invention may be carried into effect: tion of unsaturated aliphatic aldehydes by means Example 1 of oxygen or a gas containing oxygen is carried out in the presence of a per-compound of an A mixture of 100 grams glacial acetic acid and 25 organic acid that is completely miscible with the 0.3 gram of benzoyl peroxide was prepared and 25 aldehyde. 250 litres of air was blown through at 20° C., 10 If distillation is to be resorted to for the after cc. of the resultant per-acid were added to 190 treatment to isolate the resultant acid the boil cc. of crude crotonaldehyde and air was passed ing point of the acid used must be such that it through this mixture in a ?nely divided form at 30 can be separated readily from the resultant acid 20 litres per hour. During this process the liquid 30 and must also be distillable without decomposi was kept at 20° C. by external cooling. Accord tion. Acetic acid has been found to be particu ing to the efficiency of the cooling the rate of air larly suitable, but other acids having the afore has to be adjusted so that the reaction tempera mentioned properties e. g. propionic acid and ture does not exceed 25 to 27° C. After about 24 35 butyric acid may be employed. The presence of hours, crystals of crotonic acid separate, indi- 35 the acetic or other saturated fatty acid also eating that the crotonic acid content in the mix reduces the formation of compounds which act ture is above 80 per cent by volume. The crystals as inhibitors. This latter action is especially pro of crotonic acid are then separated by ?ltration. nounced when the crotonaldehyde to be oxidised New crotonaldehyde may then be added to the 40 is not quite dry or has been standing for a pro remaining liquid and the process may be con- 40 longed period. tinued as before. The oxidation should be effected at room tem- ' As an alternative to ‘?ltration, the crotonic acid perature or at moderate temperatures for ex maybe recovered from the reaction mixture by ample between 60° C. and 100° C. and preferably distilling 01f the remaining crotonaldehyde and 45 below the boiling point of the aldehyde to be ?nally the acetic acid under reduced pressure. 45 oxidised. The distillation has however to be conducted with Oxidation may be effected under ordinary great precaution as a sudden rise of temperature pressure but increased pressure may be employed may occur due in part to rapid decomposition of if desired. Small amounts of an oxidation ca the per-compounds present in the reaction mix 50 talyst or an oxygen carrier such as manganese ture and to other exothermic by-reaction. 50 acetate, copper acetate, copper crotonate and the Example 2 like may be added to the reactants. Organic oxygen carriers such as benzoyl peroxide are par A mixture of 200 cc. of crotonaldehyde and 25 ticularly advantageous. > cc. of acetic acid and 0.03 gram benzoyl peroxide 55 The amount of acid added to the aldehyde may was run down a packed column up which a cur- 55 2 2,183,325 rent of air was passing. The rate of the aldehyde 3. The method according to claim 1 in which ?ow was adjusted to 10 cc. per hour and the rate the aldehyde employed is crotonaldehyde. of the air flow was adjusted to 10 litres per hour 4. The method of converting unsaturated ali thereby ensuring that the temperature in the phatic aldehydes into their corresponding acids column did not exceed 80° C. The solution of by oxidation which consists in subjecting the resultant crotonic acid in the acetic acid and aldehyde to the action of a gas containing oxygen some crotonaldehyde, which collected at the base in the presence of a per-compound of an organic of the column, was distilled under reduced pres acid that is completely miscible with the alde sure to isolate the crotonic acid. hyde. 10 What I claim is: 5. The method of converting crotonaldehyde 1. The method of converting unsaturated ali to crotonic acid by oxidation which comprises phatic aldehydes into their corresponding acids subjecting crotonaldehyde to the action of an by oxidation which consists in subjecting the oxygen-containing gas selected from the class aldehyde to the action of oxygen in the presence consisting of oxygen and air, in the presence of 15 of a per-compound of an organic acid that is per-acetic acid. completely miscible with the aldehyde. 2. The method according to claim 1, in which HANN S PETER STAUDINGER. the per-compound used for assisting the conver sion is per acetic acid.