Step 1 Preparation of 5,6-O-isopropylidene-L-ascorbic acid
176 g (1 mol) of ascorbic acid and 870 g (15 mol) of acetone were sequentially added into a 5L reactor, stirred for 10 minutes, 6.5 g (0.05 mol) of oxalyl chloride was added dropwise under ice-cooling conditions, and reacted at 30°C for 9 hours. After the reaction was completed, the filter cake and filtrate A were obtained after filtration. The filtrate A was used for later use. The filter cake was washed with 80 g of acetone and dried to obtain 195.1 g of 5,6-O-isopropylidene-L-ascorbic acid with a yield of 90.2%.
Add calcium oxide 74 grams (1.32mol) in filtrate A, stir 3 hours, filter, and filtrate is dried 12 hours with 90 grams of molecular sieves, filters, and obtains the acetone filtrate B after treatment, and this acetone filtrate B can utilize again.
176 g of ascorbic acid was added to the treated acetone filtrate B, stirred for 10 minutes, 6.5 g of oxalyl chloride was added dropwise under ice-cooling conditions, and the reaction was carried out at 30° C. for 9 hours. After the reaction, filter again to obtain the filter cake and filtrate C, wash the filter cake with 80 g of acetone, and dry to obtain 200.5 g of 5,6-O-isopropylidene-L-ascorbic acid, with a yield of 92.7%.
Add 74 grams of calcium oxide to the filtrate C, stir for 3 hours, filter, and dry the filtrate with 90 grams of molecular sieves for 12 hours, filter to obtain the acetone filtrate D, which can be reused.
Add 176 g of ascorbic acid to the dried acetone filtrate D, stir for 10 minutes, add 6.5 g of oxalyl chloride dropwise under ice-bath conditions, and react at 30° C. for 9 hours. After the reaction was completed, filter, wash the filter cake with 80 g of acetone, and dry to obtain 206.1 g of 5,6-O-isopropylidene-L-ascorbic acid, with a yield of 95.3%.
Step 2 Preparation of 3-O-ethyl-5,6-O-isopropylidene-L-ascorbic acid
Add 216.2 grams of 5,6-O-isopropylidene-L-ascorbic acid prepared in step 1 into a 5L reactor, add 430 grams (9.3mol) of ethanol, stir for 30 minutes, add 131 grams of sodium bicarbonate (1.56 mol), slowly added dropwise 200 grams of diethyl sulfate (1.3mol), gradually heated to 55°C, reacted at this temperature for 6.5 hours, then concentrated the reaction solution, added 250 grams of dichloromethane (2.94mol) to dissolve the product, After filtration and recrystallization, 203.5 g of 3-O-ethyl-5,6-O-isopropylidene-L-ascorbic acid was obtained, with a yield of 83.4%.
Step 3 Preparation of Ascorbic Acid Ethyl Ether
Add 244 grams of 3-O-ethyl-5,6-O-isopropylidene-L-ascorbic acid prepared in step 2, 320 grams of ethanol, stir to dissolve, 55 grams of hydrogen chloride ethanol solution, water 30 grams, heated to 55°C, reacted for 4 hours, concentrated the reaction solution to one-third of the original volume, added an equal volume of dichloromethane for recrystallization, and obtained 190.4 grams of 3-O-ethyl ascorbic acid ether, with a yield of 93.3%; continue Recrystallized with dichloromethane and ethanol (volume ratio 2:1), to obtain 177.5 g of 3-O-Ethyl-L-Ascorbic Acid (molecular weight 204.18), yield 86.9%.