X. THE CHEMICAL CONSTITUENTS OF PLANTS 203 



camphor, G 10 H 16 O and menthone, C 10 H 18 O, may serve as examples of 

 the ketones. 



Borneol occurs in Borneo camphor and can be obtained as crystals 

 which melt at 203 and boil at 212. It can be obtained from cam- 

 phor by reduction with sodium and, conversely, by oxidation yields 

 camphor. 



Terpineol occurs in several isomeric forms and has been found in 

 oil of cardamons, etc. 



Menthol occurs in oil of peppermint. It melts at 43, boils at 212 

 and has a specific gravity of 0*89. 



These alcohols form esters with organic acids, and their acetates, 

 in particular, often occur in nature. 



Camphor occurs in the wood of Laurus camphor a. It is a colour- 

 less crystalline substance, soluble in alcohol, melting at 175 and boil- 

 ing at 204. It has a rotation of + 44. Its constitution has been 

 the subject of much investigation and has been proved by Bredt x and 

 Aschan 2 to be as follows : 



showing it to be a ketone. Borneol is the corresponding alcohol. 



3. Benzene Derivatives. A hydrocarbon, para-methyl isopropyl 

 benzene, known as cymene, C 6 H 4 (CH 3 )(C 3 H 7 ), occurs in Koman cara- 

 way oil. 



Many phenols and phenolic ethers occur in essential oils, among 

 which the most important are 



Eugenol, allyl oxymethyl hydroxybenzene, C 6 H 3 (C 3 H^(OCH 3 )OH, 

 found in oils of cloves, allspice, bay and cinnamon, a liquid of specific 

 gravity 1-07, boiling at 247 ; 



Safrol, allyl dioxymethylene benzene, C 6 H 3 (C 3 H 5 ):(O.CH 2 .O), occur- 

 ring in oils of camphor and sassafras ; 



Apiol, dimethoxydioxymethylene allyl benzene, C 6 H(OCH 3 ) 2 : 

 (O.CH 2 .O).(C 3 H 5 ), found in parsley and dill oils; 



Thymol and carvacrol, methyl isopropyl hydroxybenzene, 

 C 6 H 3 (CH 3 )(C 3 H 7 )OH, occurring in thyme oil. The former is a 

 solid, melting at 44 and boiling at 230, the latter a thick oil boiling 

 at 236. 



Of aldehydes of benzene derivatives the following occur na- 

 turally : 



Benzaldehyde, C 6 H 5 COH, is the chief constituent of the oils of 

 bitter almonds, peach and plum kernels, and of other members of the 

 prunus family. Its specific gravity is 1-05 and it boils at 179. 



1 Ann., 289, 15 ; Jour. Chem. Soo., 1894, Abstracts, i. 141. 



2 Ann., 316, 196; Jour. Chem. Soc., 1901, Abstracts, i. 477. 



