4．
甲基丙烯酸甲酯是世界上年产量超过\(\rm{100}\)万吨的高分子单体，旧法合成的反应是\(\rm{(CH_{3})_{2}C=O+HCN\xrightarrow{{}}}\) \(\rm{(CH_{3})_{2}C(OH)CN}\)，\(\rm{(CH}\)\(\rm{{\,\!}_{3}}\)\(\rm{)}\)\(\rm{{\,\!}_{2}}\)\(\rm{(OH)CN+CH}\)\(\rm{{\,\!}_{3}}\)\(\rm{OH+H}\)\(\rm{{\,\!}_{2}}\)\(\rm{SO}\)\(\rm{{\,\!}_{4}\xrightarrow{{}}}\)\(\rm{CH}\)\(\rm{{\,\!}_{2}}\)\(\rm{=C(CH}\)\(\rm{{\,\!}_{3}}\)\(\rm{)COOCH}\)\(\rm{{\,\!}_{3}}\)\(\rm{+NH}\)\(\rm{{\,\!}_{4}}\)\(\rm{HSO}\)\(\rm{{\,\!}_{4,}}\)\(\rm{90}\)年代新法的反应是：\(\rm{CH}\)\(\rm{{\,\!}_{3}}\)\(\rm{C≡CH+CH}\)\(\rm{{\,\!}_{3}}\)\(\rm{OH+CO}\)\(\rm{\xrightarrow{{Pb}}}\)\(\rm{CH}\)\(\rm{{\,\!}_{2}}\)\(\rm{=C(CH}\)\(\rm{{\,\!}_{3}}\)\(\rm{)COOCH}\)\(\rm{{\,\!}_{3}}\)与旧法比较，新法的优点是