— 144 — 



(20 mm.), dgg 0,9236, [«] D + 83,2° (4,5°/o solution in ethyl acetate), n D 1,4783. 

 When fZ-J 3 -/>-menthenol-8 was boiled with oxalic acid it yielded ri-J 3:H(0 -/>- 

 menthadiene, possessing the following constants: dj- ° 0>8649*), ["] D -f 100,0°, 

 n D 1,4965. It is not yet certain whether the rotation mentioned above re- 

 presents the maximum value, because in the treatment with oxalic acid 

 partial racemisation is not impossible. 



In addition to the above, Perkin-) has produced synthetically zT'-o-men- 

 thenol-8, J 5:8(9) - and z! 6:8(9; -o-menthadiene, cis- and trans-A 8 -o-menthenol-8, 

 zf 4 -o-menthenol-8, as well as cis- and fr<ms-zl 3:8(!, '-6>-menthadiene and A i: *'- ); -o- 

 menthadiene. 



As the starting point of the synthesis of A r> - and z^-o-menthenol, 

 Perkin employed 6-hydroxy-o-toluic acid 3 ) which, when reduced, yields a 

 mixture of the cis- and frYms-modifications of l-methylc?/c7ohexane-6-ol-2- 

 carboxylic acid which, under the influence of fuming hydrobromic acid, 

 yields 6-bromo-l-methylq/c7ohexane-2-carboxylic acid. 



Treatment of the ethyl ester of this acid with diethylamide results 

 in a mixture of ethyl 1-methyl-J 5 - and ethyl l-methyl-zl 6 -c#c7ohexene-2-car- 

 boxylates; the free acids can be separated by fractional esterification. 

 The ethyl l-methyl-zl 5 -e^cZohexene-2-carboxylate was allowed to react 

 with methyl magnesium iodide, the reaction giving rise to zl r> -o-menthenol-8: 

 b. p. 198 to 200° (734 mm.), df£ 0,9405, n D 1 ,4792. The corresponding A" :8(9) - 

 o-menthadiene boiled between 170 and 171 ° (765 mm.): d~§ 0,8490, n D 1,4778. 



From l-methyl-z1 6 -q/dohexene-2-carboxylate, Perkin, by the same pro- 

 cess, obtained zl 6 -o-menthenol-8: b. p. 200 to 202° (734 mm.). The A« iS ™-o- 

 menthadiene boiled at 170 to 171°: d~ 0,8481, n D 1,4758. 



The menthenols and menthadienes of the cis- and trans-modifications 

 of l-methyl-zl 3 -q/cfohexene-2-carboxylic acid were prepared by the usual 

 method. /mns-/d 3 -o-menthenol-8 boils at 110 to 111° (30 mm.), trans- 

 J 3:8(9) -o-menthadiene boils at 170° (760 mm.): d|| 0,8477, n D 1,4749. cis- 

 J 3 -o-menthenol-8 has b. p. 107 to 108° (30 mm.), m-J 3:8(9) -o-menthadiene 

 boils at 169 to 170° (762 mm.); df£ 0,8507, n D 1,4825. 



From l-methyl-zl 4 -ci/c*7ohexene-2-carboxylic acid, Perkin obtained A l -o- 

 menthenol-8: b. p. 110° (30 mm.) m. p. of the phenylurethane: 119 to 120°. 

 The zl 4:8(9) -o-menthadiene boiled at 160 to 171°. 



On /^-benzyl-^-glucoside see p. 139. 



Aldehydes. 



Citral. In previous Reports we have dealt with Semmler's 4 ) researches 

 into the formation of enolic acetates from aldehydes which, adjoining 



*) As the quantity of substance available was only small, this^determination is not exact. 



2 ) Journ. chem. Soc. 99 (1911), 727, 741. 



s ) Baudisch and Perkin, Journ. chem. Soc. 95 (1909), 1884. 



*) Report April 1909, 128; October 1909, 183. 



