1559rch20359-37210/18/054:24Page372 EQA 372 chapter 20 CARBOXYUC ACID DERIVATIVES Second reaction:An ester can serve asa source of acylium ion.too CaHsO-compound A again 0--0 oaee to give Third reaction sequence: C.H 63.(e) 64.(a 65.(d 66.b)Second reaction: An ester can serve as a source of acylium ion, too. But what else can happen? What is this product C, with the formula C8H10? Look at the NMR: Five benzene hydrogens, and CH2 and CH3 groups upfield—looks like ethylbenzene! How? The Lewis acid complexed oxygen is a good leaving group, so we can propose the following: Third reaction sequence: 63. (e) 64. (a) 65. (d) 66. (b) C10H10O3 O CO2H O C10H12O2 CO2H C10H11ClO C10H10O COCl which, of course, can go on to undergo another acylation to give C Cl3Al O O  D O C8H8O compound A again O CH3C O Cl3Al O O  372 • Chapter 20 CARBOXYLIC ACID DERIVATIVES 1559T_ch20_358-372 10/18/05 4:24 Page 372