Method for preparing sildenafil citrate

The invention discloses a method for preparing sildenafil citrate. The preparation method comprises the following steps: (a) adding a compound II into chlorosulfonic acid for a reaction to generate anintermediate III; (b) reacting the intermediate III with N-methyl piperazine to generate a crude sildenafil product; (c) recrystallizing the crude sildenafil product to obtain a pure sildenafil product; and (d) carrying out a salifying reaction on the pure sildenafil product to obtain sildenafil citrate. The method is beneficial for industrial production. 本申请公开了一种制备枸橼酸西地那非的方法。所述制备方法包括：(a)将化合物II加入氯磺酸中进行反应，生成中间体III；(b)使中间体III与N-甲基哌嗪进行反应，生成西地那非粗品；(c)西地那非粗品经重结晶得到西地那非纯品；(d)西地那非纯品再经成盐反应得到枸橼酸西地那非。本发明的方法有利于工业化生产。