178 PRACTICAL ORGANIC CHEMISTRY off the carbon tetrachloride (b.p. 77°) at atmospheric pressure. Distil the residue at water-pump pressure. The fraction coming over below about 58°/i4 m.m. is unchanged ethyl crotonate. Collect the fraction boiling at 98-99°/14 m.m. This is pure ethyl y-bromocrotonate, a colourless, mobile liquid having a strong pleasant odour. Yield, 25 g. Sulphonation. A further difference between aliphatic and aromatic hydrocarbons is that only the latter are capable of direct suiphonation. Thus benzene when heated with concentrated sulphuric acid gives benzenesulphonic acid, a reaction which proceeds more readily, however, if chlorosulphonic acid is used instead of sul-phuric acid: an excess of chlorosulphonic acid however may convert the sul-phonic acid into the sulphonyl chloride (cf. p. 181). C 6 H 5 H + HOSO 3 H -> C 6 H 5 SO 3 H + H 2 O C 6 H 5 H + ClSO 3 H -> C 6 H 5 SO 3 H + HCl Aromatic sulphonic acids are frequently difficult to obtain pure, since they
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This note was uploaded on 09/19/2011 for the course CHM 2211 taught by Professor Castalleano during the Fall '06 term at University of Florida.