General procedure for the synthesis of 4-(dimethylamino)o-hydroxybenzaldehyde from N,N-dimethylformamide and 3-hydroxy-N,N-dimethylaniline: 13.8 g (0.1 mol) of a mixture of 3-hydroxy-N,N-dimethylaniline and 16.0 g (0.22 mol) of N,N-dimethylformamide was slowly added dropwise at 20-40 °C, followed by the addition of methylsulfonyl chloride (0.125 mol), and the rate of titration was controlled to keep the reaction temperature from exceeding 40 °C. After the titration was completed, the reaction was stopped and the reaction temperature was reduced. After the dropwise addition, the reaction mixture was stirred at 50 to 100 °C for 1.0 hour. After completion of the reaction, the reaction solution was cooled to 30 °C and hydrolyzed by adding an appropriate amount of water. After filtration and washing with a small amount of water, 15.0 g of 4-N,N-dimethyl-2-hydroxybenzaldehyde was obtained with a yield of 90.9% and a purity of 95.5%.
[1] Chemistry - An Asian Journal, 2010, vol. 5, # 9, p. 2053 - 2061
[2] Patent: CN104262253, 2017, B. Location in patent: Paragraph 0049; 0050; 0051; 0052
[3] Molecules, 2009, vol. 14, # 12, p. 4838 - 4848
[4] Journal of Molecular Structure, 2018, vol. 1154, p. 373 - 381
[5] Chemical Papers, 2010, vol. 64, # 6, p. 806 - 811
