Patent GB-858665-A (GB)
Title: Process for the simultaneous manufacture of aliphatic ª‡-hydroxy-and ª‡:ª‡-dihydroxydi-carboxylic acids and mixtures of phenols
Inventor: DOST GERHARD
IPC: C07C51/00
Filed: 1957-02-26
Abstract: Aliphatic a -hydroxy and a , a 1-dihydroxy dicarboxylic acids containing at least 5 carbon atoms and mixtures of phenols are obtained by heating a substance containing lignin and one or more polysaccharides, e.g., wood, with an aqueous solution of an alkali metal hydroxide or with an aqueous suspension of an alkaline earth metal hydroxide containing 12 to 25% weight to volume, of the alkali metal or alkaline earth metal hydroxide, the amount by weight of such hydroxide being at most equal to that of the substance containing lignin and polysaccharides, under pressure and at a temperature of 160 DEG  to 250 DEG  C. and isolating the hydroxydicarboxylic acids and mixtures of phenols from the resulting reaction mixture.  It is advantageous to use a metal of the second sub-group of the Periodic System or an oxide of such metal, e.g. cadmium oxide, as catalyst. The alkaline reaction mixture is worked up by first freeing it by filtration from a sediment consisting of the catalyst (if used) and undissolved organic matter and then neutralising the solution by the introduction of carbon dioxide.  The unreacted portion of lignin which is precipitated is filtered off and the remaining solution is extracted with a solvent for the liberated phenols, e.g. ether or ethyl acetate.  The solvent is then distilled off to leave the phenols as residue.  The remaining unextracted reaction mixture is then acidified with a mineral acid and after separating the precipitate formed the mixture is extracted with a suitable solvent, e.g. ether or ethyl acetate and the aliphatic a -hydroxy and a , a 1-dihydroxy decarboxylic acids may then be isolated in the form of their sparingly soluble zinc or calcium salts.  Alternatively, the crude acid mixture obtained by distilling off the solvent from the extract may be converted into an ester, e.g. by reaction with an alcohol such as methanol or ethanol in the presence of a mineral acid or by reaction with p  diazomethane.  The methyl or ethyl esters of the hydroxy dicarboxylic acids may then be isolated by fractional distillation and the ester fractions may be further separated by treating with alcoholic ammonia to form the corresponding acid amides, which are then separated by fractional crystallisation. Specified ester fractions obtained from the esterified mixture are methyl acetate with some methyl formate, methyl lactate, methyl oxalate, methyl a -hydroxybutyrate and methyl glycollate, methyl succinate, methyl a -hydroxy glutarate, and methyl dihydroxyadipate. Examples are given for the treatment of (1) powdered beech wood and (2) powdered pine wood respectively with sodium hydroxide solution in the presence of cadmium oxide to yield in the case of (1) a mixture of phenols containing guaiacol, and a mixture of acids comprising formic, acetic, and lactic acids and a -hydroxyglutaric acid and a , a 1-dihydroxy-adipic acid which are both isolated in the form of their calcium salts. Similar products are obtained in (2).  It is stated that the phenols obtained from beech wood include guaicol, creosol, pyrogallol-1, 3-dimethyl ether, methyl pyrogallol-1 : 3-dimethyl ether, acetosyringin and homologues of pyrocatechol, and that the phenols from pine wood include guaiacol, creosol, ethylguaiacol, acetovamillin and pyrocatechol.  The individual phenol may be separated by distillation.  Specification 858,286 is referred to.