C2H5OH＋（H2SO4,加热）＝C2H4＋H2O,C2H4＋Br2＋＝CH2BrCH2Br,CH2BrCH2Br＋2NaOH＋（C2H5OH）＝C2H2,C2H2＋HCl＝CH2CHCl,nCH2CHCl＝聚氯乙烯.括号内是催化剂!