Resolution of phyto-hormone acids 



Zimmerman. However, no similar report has appeared on the branched or 

 a-series. 



Racemic a-(l-naphthyl)propionic acid was first described by Blicke. 

 The method we used was to react naphthalene with a-bromopropionyl 

 bromide in the presence of a catalyst and extract the product from the mainly 

 unreacted naphthalene remaining. 



There are several other methods of arriving at a- (1-naphthyl) propionic 

 acid but after attempting the production by such strictly laboratory scale 

 methods as those involving the Knoevenagel reaction and those including 

 Grignard and Friedel Craft techniques, we found our method more 

 convenient : 



CH3— CH2— CO 



Br4 . o/^TT ^TTTi r^r^Ty^ '^lo^s 



^O — '-> 2(CH3- CHBr- COBr) -^^^ 

 CH3— CH2— CO CH3 



CH • COOH 



The product is readily dissolved out from the reaction mixture with 

 bicarbonate solution and best purified from the crude acid by esterification 

 and distillation in vacuo of the ethyl ester followed l:)y saponification. It has 

 m.p. 149-3- 150-0°. To resolve the racemic acid we naturally first attempted 

 to accomplish this by the means of the ( + ) and ( — ) amphetamides as above 

 outlined. There was no difficulty in this reaction, but it was found that the 

 hydrolysis was extremely difficult in this case as compared with a-(2:4- 

 dichlorophenoxy)propionic amphetamide. In the latter case although the 

 alkaline saponification was impossible, the acid method as employed by 

 Manske in his work on a-naphthylacetonitrile gave good results. However, 

 with the amphetamides of naphthylpropionic acid it was found that the only 

 way to hydrolyse them was by heating at 180°C for 48 hours with syrupy 

 phosphoric acid and acetic acid. As might have been expected, this drastic 

 treatment racemized the compound almost completely so that nothing was 

 accomplished. 



We reverted to the older methods and fovmd that a good separation could 

 be obtained using the cinchonine salt in an aequeous methanol medium. 

 The cinchonine salt of the (^) acid crystallizes out first and is pure after 

 three recrystallizations. The (-|-) acid is obtained without any difficulty 

 from the mother liquors in the usual way. 



The ( — ) acid has the following characteristics: 



m.p. 68-9°, [a]^^ = —118-1 {c = 3-168 in methanol) 



— 141-3 {c = 3-87 in acetone) 



— 131-7 {c= 3-863 in chloroform) 

 -172-0 {c = 2-419 in benzene) 

 -35-3 {c = 2-25 in NaOH sol.) 



The (+)-acid has m.p. 67-5-68° and [aj^c^ +1 17-5 (c = 2-00 in methanol). 



215 



