48 



AROMATIC COMPOUNDS 



These hydroxybenzoquinones are orange, crystalline solids which are readily re- 

 duced by sodium dithionite to colorless hydroquinones. Alkaline solutions are blue -purple 

 in color. Naturally occurring quinones are extensively reviewed by Thomson (3). 



PHENYLPROPANE COMPOUNDS IN GENERAL 



A large number of natural aromatic compounds may be described as phenylpropane 

 derivatives since they have a benzene ring attached to C-1 of a three carbon chain: 



\ /; 



c— c— c 



A few other compounds are found which have a phenyl group attached to the middle carbon 

 of the C3 chain. Some of these may be formed by rearrangement of 1 -phenylpropane com- 

 pounds, whereas others seem to be more closely related to the monoterpenoids. Examples 

 of these two types of 2-phenylpropane derivatives are, respectively, tropic acid (4) and 

 thymoquinone: 



Q 



COOH 



I 



CH 

 I 

 CHoOH 



Tropic Acid 



Thymoquinone 



Other 1-phenyl propane derivatives will be discussed in more detail in following sections 

 of this chapter. The flavonoids (Chapter 9) also contain a phenylpropane group joined to 

 a phloroglucinol group. Geissman (5) has reviewed the phenylpropane derivatives of plants. 



OPEN-CHAIN PHENYLPROPANE DERIVATIVES 



Some open-chain phenylpropane derivatives are among the best-known and most 

 widespread natural aromatic compounds. Most of them may be described as hydroxylated 

 cinnamic acid derivatives: 



CH=CHCOOH 



Cinnamic Acid 



The variations on this basic structure are distinguished by different patterns of ring hy- 

 droxylation or methoxylation and modification of the carboxyl group by esterification or 

 reduction to an aldehyde or alcohol. There are also other open-chain phenylpropanes 



