Preparation of 2-hydroxyarylaldehydes
(Rated as: excellent)
Preparation of 2-hydroxyarylaldehydes.
2-Hydroxyarylaldehydes, e.g., (I; R1-R4 = H, halo, alkyl, cycloalkyl, aralkyl, aryl, alkylaryl, alkoxy, aryloxy, acyl) were prepd. by reacting Mg bishydrocarbyloxides, derived at least in part from hydroxyarom. compds. having ³1 free position ortho to the OH group, e.g., (II), with formaldehyde or a formaldehyde-liberating compd. under substantially anhyd. conditions at 50-700 mm Hg abs. Thus, a soln. prepd. from Mg, MeOH, and 4-nonylphenol in PhMe was treated with paraformaldehyde in PhMe at 75° and 380-260 mm Hg over 2 h with removal of PhMe and volatile byproducts by distn. to give 85% 5-nonylsalicylaldehyde. The yield at atm. pressure and 95-100° was 78.8%.
Methanol (225 g) and toluene (108 g) were charged to a reaction vessel followed by particulate magnesium (2.92 g). An activator solution (10 g) was added to activate the magnesium and the mixture was heated to reflux temperature (65 DEG C.) to achieve magnesium dissolution with evolution of hydrogen gas. The mixture was maintained at reflux temperature for 0.5 h and then further magnesium was added in four portions (4.times.2.92 g) over a total period of 1.5 h, each portion being added once hydrogen evolution from the previous portion had subsided. The mixture was then heated under reflux for a further 1.5h to ensure complete magnesium dissolution and 4-nonylphenol (224 g) was added. The activator solution was taken from a composition (1116 g) containing nonylphenol magnesium salt (461 g), magnesium methoxide (17.3 g), toluene (194 g) and methanol (443.7 g).
Toluene (208 g) was added and methanol-toluene azeotrope (303 g) was removed by distillation under reduced pressure (350-400 mm Hg) with fractionation, distillate being removed up to the point where the reaction mixture viscosity increased and the reaction temperature reached 75 DEG C. at 380 mm Hg.
An agitated slurry of paraformaldehyde (92.8 g) in toluene (130 g) was added to the resulting toluene solution of the nonylphenol magnesium salt under reduced pressure at 75 DEG C. over 2 h with removal of toluene and volatile by-product distillates. The reaction temperature was maintained at 75 DEG C. throughout the addition by reducing the pressure from 380 to 260 mmHg. On completion of paraformaldehyde addition, heating was continued at 75 DEG C. under reduced pressure (260 mm Hg) for 1 h to ensure completion of reaction and the mixture was then cooled to 30 DEG -40 DEG C.
The reaction mixture was drowned out into a mixture of cold water (750 g) and sulphuric acid (122.5 g), maintaining the temperature of the mixture between 30 DEG C. and 40 DEG C. The whole mixture was stirred at 30 DEG -40 DEG C. for 2 hours then allowed to settle and the upper (organic) layer was separated from the lower (aqueous) layer.
The organic layer was washed with water (2.times.250 g) until acid-free and toluene was then removed by distillation under reduced pressure at up to 90 DEG C. to leave the crude 5-nonylsalicylaldehyde as a yellow oil (253 g, 83.3% strength, 85% yield from nonylphenol). The aldehyde was purified by distillation at 205 DEG -210 DEG C./20 mm Hg.
When the same reaction is performed in toluene at atmospheric pressure and a temperature of 95 DEG -100 DEG C., 5-nonylsalicylaldehyde is obtained in 78.8 yield (78.8% strength).
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