ацетальдегид (Н2,кат)→x1→бромэтан→бутан(t,кат, +2Br2)→x3

CH3CHO + H2=CH3CH2OH
CH3CH2OH_+ HBr=CH3CH2Br+ H2O
2CH3CH2Br + 2Na=C4H10+2NaBr
C4H10+ 2Br2=C4H9Br + HBr

алкин