svxiii i:sis oi- i)i:i'sii)i:s. 14:5 



aciiK'ous alkali, and more slowly with normal ammonia solution; 

 hut in the latter case the group splits off. not as carbonate, hut 

 as urethane Nil... C(^OCH.^. Neutral alkali carhonate acts even 

 more slowly, whilst hicarhonate is apparently indifferent, and 

 hence is useful for dissolving out the acids. Partial removal also 

 takes place with smaller quantities of alkali, the para groups 

 being first attacked. By this means the mono-methyl carbonate 

 compounds can be prepared from the di methyl carbonato com- 

 pounds. 



The chlorides of these methyl carlxMiato carboxylic acids 

 are prepared by the action of PCI-, either by gentle heat or shaking 

 the acid with PCI,- and dry chloroform. Cienerally speaking, they 

 crystallise well, and show the reactions of acid chlorides, such as 

 benzoyl chloride. By replacement of the methyl carbonato group 

 with the original phenol group, the acid chlorides themselves are 

 obtained. The latter have been obtained directly by M. Meyer, 

 but the ])roducts he obtained do not crystallise, remaining as oils, 

 and cannot be compared in importance with those obtained as 

 above by Fischer's method. Further, the chlorides of the com- 

 pletely methylated or acylated phenol carl)oxylic acids have been 

 known for a long time, and are stable enough to serve for syn- 

 thetic purposes, but the removal of the methyl or acyl groups 

 afterwards is difficult. 



These methyl carbonato acid chlorides have been used for 

 the following syntheses : — 



1. With alcohol they form esters, which on subsecjuent 



saponification with alkali, are changed to the esters of 

 the free phenol carboxylic acids. This reaction is of 

 especial importance in the case of the polybasic alcohols 

 of the sugar class, as will be exemplified later. 



2. With the amino acid esters in acjueous alkaline solution, 



they coui)le themselves directly, as shown in the case 

 of para hydroxy hippuric acid, given above. By this 

 means the isomeric ortho-salicyl-uric acid has also been 

 prepared. 



3. In the presence of aluminium chloride direct union with 



benzene takes [)lace as shown in the synthesis of para 

 oxy benzo-phenone : thus — 



/ O. COOCH. / O. COOCH., 



Cell, -f CJT, = C,H, + HCl 



■^ COCl \CO. C,H, 



saponification removing the methyl carbonato group. 

 It is noteworthy here that jjyrogallol carboxylic acid 

 yields 2.3.4. trihydroxy-benzo])henon identical with' 

 alizarin yellow A, whose formula CO | C,.H. (C)ll);5]... 

 is now conclusively established. 



4. The free phenol carboxylic acids also react directly with 



the chloride forming di-depsides, as already shown, 

 and similarly for tri- and tetra-depsides. 



