Конденсация кислот с бензолами в присутствии полифосфорной кислоты.

(примечание: эта процедура общая для всех кислот,в т.ч. для уксусной)

SYNTHESIS: A solution of 110 g p-dimethoxybenzene and 102 g valeric acid in 168 g polyphosphoric acid was heated on the steam bath for 3 h, giving a deep red homogeneous solution.  This was poured into 1 L H2O with good stirring.  The strongly acidic, cloudy suspension was extracted with 3x200 mL CH2Cl2, the extracts pooled, washed with 4x150 mL 5% NaOH, and finally once with dilute HCl.  The solvent was removed under vacuum, and the residual amber oil cooled overnight at 0 deg C. Some 30 g of crystalline, unreacted dimethoxybenzene were removed by filtration, and the 85 g of residual oil distilled at the water pump. Another 15 g of di-methoxybenzene came over as an early cut, but the fraction boil-ing at 184-192 deg C (mostly 188-192 deg C) weighed 53.0 g and was reasonably pure 2,5-dimethoxyamylophenone.  The reaction of the acid chloride of valeric acid with p-dimethoxybenzene and anhydrous AlCl3 in CH2Cl2 (parallel to the preparation of the butyrophenone analog, see DOBU) gave an inferior yield (23.2 g from 92 g dimethoxybenzene), but did provide a sizeable sample (12.2 g) of 2-hydroxy-5-methoxyamylophenone from the basic washes of the crude reaction mixture.  This pale yellow solid, after recrystallization from MeOH, had a mp of 62-62.5 deg C.  Anal. (C12H16O3) C,H.