32 



HYDROCARBONS 



[6 A-F. 



bacher, Ann. 47, 120 ; Van Romburgh, 

 Bull. Soc. 36, 550 ; Griner, Ann. Chim. 

 [6] 26, 367 ; Aronstein, Ann. Suppl. 3, 

 180; Wag'ner, Journ. Russ. Soc. 16, 

 31 7 ; Wohl and Neuberg, Ber. 32, 1352), 

 dibromacrolei'n = dibrompropionic alde- 

 hyde by combination with bromine 

 (Aronstein, loc. cit. 185 ; Henry, Ber. 7, 

 1 1 12; Linnemann and Penl, Ber. 8, 

 1097), and the ethyl diacetal by con- 

 densing the aldehyde with formimino- 

 ether (Claisen, Ber. 31, 1015). The 

 diacetal on treatment with alcoholic 

 potash gives the diacetal of propargyl- 

 aldehyde = propinal, the latter being 

 obtained by the action of dilute sul- 

 phuric acid on the diacetal (Claisen, loc. 

 cit. 1022). Propinal is decomposed by 

 aqueous alkali into acetylene and formic 

 acid (Claisen, loc. cit.}. From acetylene 

 to benzene as above. 



The synthetical processes for the pro- 

 duction of cymene are the following : 



[A.] From benzene, methyl [13], and 

 normal or isopropyl alcohol [15 ; 16]. 

 Benzene and normal or isopropyl bromide 

 or the corresponding chlorides condense 

 in the presence of aluminium bromide 

 or chloride respectively to form isopropyl- 

 benzene = cumene (Gustavson, Ber. 11, 

 1251 ; R. Meyer, Journ. pr. Ch. [2] 34, 

 98; Silva, Bull. Soc. [2] 43, 317; 

 Glaus and Schulte im Hof, Ber. 19, 

 3012 : see also Kekule and Schrotter, 

 Ber. 12, 2280; Konowaloff, Journ. 

 Russ. Soc. 27, 457 ; Radziewanowski, 

 Ber. 28, 1137). 



Or monobrombenzene and isopropyl 

 iodide condense to isopropylbenzene on 

 treatment with sodium (Jacobsen, Ber. 

 8, 1260). 



Isopropylbenzene on bromination in 

 presence of iodine gives parabromiso- 

 propylbenzene (R. Meyer, loc. cit. 101), 

 and this condenses with methyl iodide 

 under the influence of sodium to form 

 cymene (Widman, Ber. 24, 439 ; 1362 ; 

 see also Jacobsen, Ber. 12, 430). 



Or toluene (see above under IX) and 

 isopropyl chloride condense to cymene 

 in contact with aluminium chloride 

 (Silva, loc. cit. 321). 



NOTE : Isopropylbenzene may also be syn- 

 thesised from toluene through benzal chloride 



bychlorination (Beilstein, Ann. 116, 336 ; Beil- 

 stein and Kuhlberg, Ann. 146, 322) and interac- 

 tion of the latter with zinc methyl (Liebmann, 

 Ber. 13, 46). Or from cumic acid [Vol. II] by 

 distillation with lime or baryta (Gerhardt and 

 Cahours, Ann. Chim. [3] 1, 87 ; 372 ; 14, 107; 

 Ann. 38, 88). Or from isobutyric aldehyde [84] and 

 pyroracemic acid (see above under XIV) through 

 isopropylisophthalic acid, which gives isopro- 

 pylbenzene on distillation with lime (Doebner, 

 Ber. 24, 1748). Or from phenyldimethylcarbinol 

 through /3-allylbenzene = methovinylbenzene 

 by dehydration ; the hydrocarbon gives isopro- 

 pylbenzene by reduction (Tiffeneau, Comp. 

 Rend. 134, 845). Also from acetophenone and 

 magnesium methiodide through methovinyl- 

 benzene and reduction (Klages, Ber. 35, 2640 ; 

 3507 ; 36, 620). See also under benzoic alde- 

 hyde (114 ; A). 



[B.] From dipentene [9] which gives 

 cymene on heating with phosphorus 

 pentoxide or cymenesulphonic acid by 

 the action of sulphuric acid. Or dipen- 

 tene (limonene) is combined with hydro- 

 gen bromide, the dihydrobromide further 

 brominated and the product debromi- 

 nated by reduction with zinc dust and 

 hydrochloric acid followed by sodium in 

 alcoholic solution (Baeyer and Villiger, 

 Ber. 31, 1401). 



[C.] From amyl alcohol [22] (crude 

 fusel oil) through the pentine or va- 

 lerylene obtained by the action of 

 alcoholic potash on the amylene bromide 

 (Reboul, Ann. 131, 238). This pentine 

 on heating to 250-260 gives a diva- 

 lerylene which is said to yield cymene 

 by the action of bromine (Bouchardat, 

 Comp. Rend. 90, 1560). 



[D.] Geraniol [36] gives terpin hy- 

 drate [C ]Q H 18 (OH) 2 . H 2 O] by the 

 action of dilute mineral acids (Tiemann 

 and Schmidt, Ber. 28, 2137), and this 

 on dehydration over sulphuric acid 

 gives terpin [C, H 18 (OH) 2 ]. The 

 latter gives a dibromide on heating 

 with bromine (C 10 H 16 Br 2 ), and this 

 gives cymene on heating with aniline 

 (Barbier, Bull. Soc. [2] 17, 17; Comp. 

 Rend. 74, 194). 



[E.] Linalool [37] gives terpin hy- 

 drate under the same conditions as 

 geraniol (Tiemann and Schmidt, loc. 

 cit.}. 



[F.] Terpineol [39] combines with 

 bromine to form a dibromide which 

 gives cymene on heating with zinc 

 dust. Or terpineol on standing in con- 

 tact with dilute sulphuric acid gives 



