190 — 



J. Houben, in collaboration with H. Doescher 1 ), has succeeded in 

 preparing this aldehyde in pure analytical form. 100 g. pinene hydro^ 

 chloride, 13 g. magnesium turnings and 100 g. ether were made to react 

 in the well-known manner, and boiled with 25 g. N-methyl formanilide in a 

 reflux condenser for 5 hours. After decomposing with ice and dilute sul- 

 phuric acid, the mixture was extracted with ether and the aldehyde separa- 

 ted from the ethereal solution by adding sodium bisulphite solution. When 

 set free from the bisulphite compound by boiling with water, and purified 

 by sublimation, the aldehyde formed white needles, m. p. 131°. 



Boiling the hydropinene aldoxime with acetic anhydride in a reflux 

 condenser gave rise to hydropinene nitrile; small needles, m. p. 163°. 

 By heating this nitrile with pyruvic acid and /2-naphthylamine, the ft- 

 naphthocinchoninic acid derivative (m. p. 294°) could be obtained. When 

 the aldehyde was oxidised in the air it yielded hydropinene carboxylic 

 acid, but it was found impossible to purify this acid by recristallisation. 

 Ethyl hydropinene carboxylate is an oil with a pleasant odour; b. p. 

 116 to 117° (12,5 mm.) d 0,976. Attempts to reconstitute the acid from 

 the ester were abortive. In order to prepare the acid in the pure form 

 the best method is to start from the anhydride, which is obtained by acting 

 with acetyl chloride upon hydropinene carboxylic acid. A mixed anhydride 

 of hydropinene carboxylic acid and acetic acid is first formed and when 

 this is heated to 200° acetic anhydride is split off, under formation of 

 hydropinene carboxylic anhydride (needles, m. p. 210°). Hydropinene car- 

 boxylic acid is prepared by boiling the anhydride with 5 °/o potash liquor: 

 m. p. 78°, b. p. 153° (13 mm.), inactive. Hydropinene carboxylic amide 

 occurs in small prisms, m. p. 138 to 139 Q , the anilide consists of silky 

 needles, m. p. 151°. Various facts indicate that hydropinene carboxylic 

 acid occurs in isomeric forms, e. g. the acid which is recovered from the 

 aldehyde crystallises much better than that obtained with magnesium and 

 carbon dioxide from the hydrochloride, and the m. p. of the former is 16° 

 higher than that of the latter. 



CH 



H 2 C 

 H 2 C 



HsCC-CH; 



CH 2 



CH-COOH 

 (CHO) 



C-CH 3 



Hydropinene carboxylic acid (-aldehyde). 



On the crystallographic-optical behaviour of the various cinnamic 

 acids, see p. 156. 



*) Berl. Berichte 43 (1910), 3435. 



