Patent GB-710489-A (GB)
Title: Manufacture of alkoxy-aldehydes
Inventor: BELLRINGER FREDERICK JAMES
Filed: 1950-05-22
Abstract: b -Alkoxy-aldehydes are made by reacting at a temperature of +30 DEG C. to - 15 DEG  C. a straight chain a ,b -unsaturated aldehyde in the presence of small amounts of alkali with a primary saturated aliphatic alcohol, keeping the molar ratio of alcohol to aldehyde during the reaction so that the alcohol is more than three mols. to one mol. of the aldehyde, neutralizing the resulting reaction mixture to a pH of 6.5-7.5 and concentrating the alkoxy aldehyde produced by rapid distillation so that the mixture to be distilled remains in contact with the heated surfaces of the evaporator for less than 20 minutes, preferably less than 10 minutes.  Acrolein and crotonaldehyde are specified aldehydes and methanol, ethanol, n-propanol and n-butanol are specified alcohols.  With acrolein the ratio of alcohol to aldehyde is preferably about 6 to 1 or more, although lower ratios, e.g. 4-5 to 1 may be used with crotonaldehyde. The excess of alcohol should be such that only 1-2 per cent of free aldehyde is present in the reaction mixture.  Tables are provided showing the fall in conversion and efficiency with increase in temperature and the increase in efficiency with increasing alcohol/aldehyde ratios for the reaction between acrolein and methanol to produce beta-methoxy propionaldehyde.  Alkaline agents may be alkali metal hydroxides or alcoholates (preferably of the alcohol used), alkaline earth metal hydroxides, e.g. barium hydroxide, and organic bases such as alkylamines or quaternary ammonium hydroxides, e.g. tetra-methyl ammonium hydroxide, and pyridine.  High concentrations of alkali, e.g. 5 gms. of sodium hydroxide per litre of reaction mixture, are conducive to good yields and may be used provided rapid cooling is effected, e.g. by reaction in a narrow tubular reactor.  Phosphoric acid is preferred for neutralization, acetic acid also being specified.  The distillation may be effected in a flash distillation to separate the alkoxy aldehyde and unreacted alcohol and aldehyde from other products or by distillation in a column to remove unreacted alcohol and aldehyde with subsequent isolation of alkoxy-aldehyde.  Distillation may also be effected with climbing or falling film evaporators in which case the contact time is reduced to a few minutes.  Preferably about 95-98 per cent of the reaction mixture is distilled, the remainder being used as a vehicle for the salt residue.  A distillate containing the alcohol and alkoxy aldehyde without the salts may readily be separated without any of the precautionary measures necessary when salts are present and is preferably effected by distilling at atmospheric pressure so that any hemiacetals formed are decomposed. Preferably copper or mild steel should not be used in the distillation equipment which may be of stainless steel or aluminium. In examples (1)-(4) methanol is reacted with acrolein or crotonaldehyde in the presence of potassium hydroxide at temperatures varying from - 9 DEG  to +5 DEG  C. to yield beta-methoxy-propionaldehyde or 3-methoxy-butyraldehyde, and in (5) ethanol is reacted with crotonaldehyde in the presence of sodium hydroxide at - 5 DEG  C. to yield beta-ethoxy-propionaldehyde, the neutralizations being effected with either phosphoric or acetic acid and the distillations effected as described above.