Patent GB-796575-A (GB)
Title: Acetaldol condensation product and process for preparation
IPC: C07D493/08
Filed: 1956-08-30
Abstract: The invention comprises a new crystalline compound of the empirical formula C8H14O3, characterized by the absence of unsaturation and of carboxyl, ester, carbonyl and hydroxy groups, the presence of an ether linkage C-O-C, and a melting-point of 114-115 DEG  C.  The compound is probably 3 : 7-dimethyl-4 : 8 : 9 - trioxabicyclo - (3 : 3 : 1) - nonane.  It may be obtained by first preparing crude acetaldol by the condensation of acetaldehyde using an alkaline catalyst, acidifying the crude acetaldol with mineral acid, heating the acidified crude acetaldol to remove the low boiling constituents of the crude and leave a residue containing the new compound, and recovering the new compound from the residue.  The preferred method for preparing the crude acidified acetaldol is first to neutralize the alkaline catalyst by treating the crude acetaldol with carbon dioxide in excess of that required completely to neutralize the alkaline catalyst and then to remove the resultant precipitate of carbonate salts.  The acidification may be effected with sulphuric acid, phosphoric acid or hydrochloric acid, a suitable concentration of sulphuric acid in the acidified acetaldol being between 0.1 and 1.0 per cent by weight.  The heating step is preferably effected by rapid passage through a boiler which heats the mixture and evaporates the material which can be distilled off at a vapour temperature between 80 DEG  and 92 DEG  C. at atmospheric pressure and delivers the liquid residue within less than 10 minutes, preferably less than 1 minute.  A circulating flash evaportor is an example of a suitable boiler. The new compound can be isolated from the residue by allowing to stand at room temperature where-upon the new compound is deposited as fine crystals which can be filtered off, preferably after adding methanol.  Alternatively, the new compound may be extracted from the residue using a non-polar solvent such as petroleum ether having a boiling range of 30-60 DEG  C.  The new compound yields crotonaldehyde when boiled in water containing a catalytic concentration (e.g. one per cent) of sulphuric acid.  In an example, crude aldol, prepared by the condensation of acetaldehyde in the presence of a caustic soda catalyst, is treated with carbon dioxide and the resultant precipitate removed; aqueous sulphuric acid is added to the neutralized aldol and the mixture is put through a small natural circulation evaporator having a steam-heated tubular boiler, the liquid feed being adjusted so that the average hold-up time of the material in the boiler is about four minutes; the evaporator is operated at 85 DEG  to 90 DEG  C. at atmospheric pressure; the new compound is isolated from the residue by cooling until crystallization takes place, by adding methanol to promote crystallization, or by extraction with 30-60 DEG  C. petroleum ether.ALSO:A new compound of empirical formula C8H14O3, which is probably 3 : 7-dimethyl-4 : 8 : 9 - trioxabicyclo - (3 : 3 : 1) nonane, (for preparation see Group IV (b)), may be used in place of crotonaldehyde in the preparation of the crotonaldehyde acetal of polyvinyl alcohol.