p-Methylacetophenone, also known as 1-(4-methylphenyl) ethanol, p-acetyltoluene, 4-methylphenyl ethyl, has the aroma similar to Hawthorn flower, and has the mixed aroma of alfalfa, honey and strawberry. It can be used to prepare lilac flavor for acacia soap, and it can also be used as fruit food flavor.
p-Methylacetophenone is a colorless needle-like crystal (or colorless to pale yellow liquid), molecular formula is C9H10O, molecular weight is 134.18, boiling point is 225oC, melting point is 28oC, refractive index is 1.5335 (20oC), relatively density is 1.0051 (20/4oC), flash point is 92oC, easily soluble in ethanol, ether, benzene, chloroform and propylene glycol, almost insoluble in water, molecular structure formula is:
Preparation Method Analysis
p-Methylacetophenone can be prepared from toluene and acetic anhydride under the catalysis of anhydrous aluminum trichloride, which belongs to C-acylation reaction. The reaction formula is:
The reaction mechanism for preparing p-Methylacetophenone is:
The possible by-product is o-methyl acetophenone, and its ratio to the main product generally does not exceed 1:20.
Laboratory Synthesis of p-Methylacetophenone
1. Chemicals and Reagents
Anhydrous toluene (20+5) mL, acetic anhydride 3.7mL (about 4.0g, 0.039mol), anhydrous aluminum trichloride 13.0g (0.098mol) concentrated hydrochloric acid, benzene, 5% sodium hydroxide solution, anhydrous chlorine calcium.
2. Experimental Procedure
- Operation Steps
Install a stirrer on a 100mL three-neck flask, a dropping funnel and a condenser tube with an anhydrous calcium chloride drying tube at the top, and the drying tube is connected to a gas adsorption device.
Quickly weigh 13.0g of anhydrous aluminum trichloride, grind it into a three-necked flask, immediately add 20mL of anhydrous toluene, slowly add a mixture of 3.7mL of acetic anhydride and 5mL of anhydrous toluene through the dropping funnel under stirring, it takes about 15 minutes to finish dripping. Then heat it in a water bath at 90~95oC for 30 minutes until no hydrogen chloride gas escapes. After the reaction solution was cooled, the three-necked flask was placed in a cold water bath, and a mixture of 30mL of concentrated hydrochloric acid and 30mL of ice water was slowly dropped into it under stirring. When it is just dropped in, it can be observed that a solid is produced, and then gradually dissolves. When all the solids were dissolved, the organic layer was separated with a separatory funnel, washed with water, 5% sodium hydroxide solution, and 15mL of water successively, and dried with anhydrous magnesium sulfate for 15 min.
Filter the dried crude product solution into a distillation flask, evaporate toluene on an oil bath, stop heating when the fraction temperature rises to about 140oC, and remove the oil bath. After cooling down slightly, use an air condenser to distill and collect fractions at 220~222oC on the asbestos net. It is also possible to stop heating when the temperature of the steam rises to 140oC. After a little cooling, change the device to a vacuum distillation device, first use a water pump to depressurize and further distill toluene, and then use an oil pump to decompress and collect fractions at 112.5oC/1.46kPa (11mmHg) and 93.5oC/98.12kPa (7mmHg). About 4~4.5g of p-Methylacetophenone can be obtained.
Pure p-Methylacetophenone is a colorless liquid with a boiling point of 225oC/98.12kPa (736mmHg), a melting point of 28oC, 
=1.5353. This experiment takes about 6~8 hours.
- Calculate Yield
The yield of this experiment is calculated according to the actual yield and the theoretical value.
- Detection and Identification of Products
Observe the appearance and properties of the product, measure the refractive index, melting point.
Industrial Production of p-Methylacetophenone
The industrial production process flow diagram of p-Methylacetophenone is as shown in Figure 1.
Fig. 1 Process flow chart of industrial production of p-Methylacetophenone
1-acylation tank; 2-dissolving tank; 3-washing and drying tank; 4-rectification tank; 5, 6-condenser; 7, 8-oil-water separator; 9-front fraction tank; 10-product tank
Add 500kg of dry toluene and 20kg of dry aluminum trichloride into a dry glass-lined reactor, stir and add acetic anhydride dropwise, and raise the temperature to about 90oC until no hydrogen chloride gas is released. Cool to room temperature, put the material into a mixture of crushed ice and concentrated hydrochloric acid, and dissolve all the aluminum chloride. Separate the toluene, wash with 10% sodium hydroxide, and wash with water twice. After drying with anhydrous calcium chloride, put it into a rectification kettle for rectification, follow up and analyze it with a chromatograph, collect products with a content of more than 97%, and obtain about 550kg of p-Methylacetophenone.
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