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2 moles) of tetrahydrofurfuryl alcohol (Note 3) is introduced from the dropping funnel at the rate of 50 cc. per hour. The product, collected in an Erlenmeyer flask which contains 30 g. of anhydrous potassium carbonate, consists of a light brown oil and a lower aqueous layer. When the reaction tube has drained, the lower aqueous layer is separated and discarded. The upper layer is fractionated through a short column, and a fraction boiling at 70-86° is collected. This consists of a mixture of water and dihydropyrane, most of which distils at 83-86°. The residue (25-35 g.) is mainly unchanged tetrahydrofurfuryl alcohol (Note 4).
The water-dihydropyrane fraction separates into two layers. The lower aqueous layer is separated and discarded. The upper layer, consisting of fairly pure dihydropyrane, is dried over 5-6 g.
of anhydrous potassium carbonate, decanted, refluxed for one hour with 2-3 g. of metallic sodium, and then distilled from sodium (Note 5). The yield is 110-118 g. of dihydropyrane, boiling at 84-86° (66-70 per cent of the theoretical amount).
1. Several varieties of technical activated alumina were used. After three or four runs the catalyst becomes covered with a brown tar and the yield of dihydropyrane decreases. The catalyst may be regenerated by igniting it at red heat until the tar is burned off. The checkers used 8-14 mesh activated alumina from the Aluminum Ore Company of America. The catalyst was reactivated at 450° by drawing a slow stream of air through it until the tar was burned off.
2. The temperature of the furnace is measured by a thermometer placed alongside the glass tube inside the furnace. The temperature should be 330-340° except in the regions about 10 cm. from each end of the furnace; here the temperatures will be 300-340°, depending on the construction of the furnace.
3. According to the submitters, Eastman’s practical grade of tetrahydrofurfuryl alcohol must be purified by distillation; the fraction boiling at 79-80°/20 mm. was used. The checkers used, without purification, tetrahydrofurfuryl alcohol obtained from the Quaker Oats Company. The yields were equally good.
4. The recovered tetrahydrofurfuryl alcohol turns yellow on standing and is unsuitable for further runs. If it is used, the yield of dihydropyrane drops to 36-38 per cent, and the catalyst must be regenerated after each run.
5. Dihydropyrane is very difficult to dry. Even after this treatment the product often contains traces of water.
3. Methods of Preparation
The procedure given above is essentially the method of Paul.1 The interaction of tetrahydrofurfuryl bromide and sodium amide
1 Paul, Bull. soc. chim. (4) 53, 1489 (1933).
gives chiefly l,4-epoxy-4-pentene and a small amount of dihydropyrane. l,4-Epoxy-4-pentene will undergo rearrangement at 380° in the presence of alumina to yield dihydropyrane.2
p,p-DIMETHYLACRYLIC ACID (Senecioic acid)
(CH3)2C=CHCOCH3 + 3KOC1 -»
(CH3)2C=CHC02K + ÑÍÑ²ç + 2KOH
2(CH3)2C=CHC02K + H2S04 ->
2(ÑÍç)2Ñ=ÑÍÑ02Í + K2S04
Submitted by Lee Irvin Smith, W. W. Prichard, and Leo J. Spillane.
Checked by Nathan L. Drake and Harry D. Anspon.
A 5-1. round-bottomed three-necked flask is equipped with a Kyrides sealed stirrer (Org. Syn. 21, 40, Note 1) and two long condensers, and the apparatus is so arranged that, if necessary, the exit water from the condensers may be quickly used to cool the flask.
In the flask are placed 200 cc. of dioxane, 100 g. (1.02 moles) of mesityl oxide, and a solution of 4.6 moles of potassium hypochlorite in 3 1. of water (Note 1), and the stirrer is started. The mixture becomes warm immediately, and within five minutes chloroform begins to reflux. When the reaction becomes very vigorous the stirrer is stopped and the flask is cooled with running water (Note 2). The stirring is resumed as soon as feasible and is continued for three or four hours, when the temperature of the ' mixture will have dropped to that of the room. Sodium bisulfite (about 5 g.) is then added to react with the excess hypochlorite (Note 3).
One of the condensers is then replaced by a dropping funnel,
2 Paul, Bull. soc. chim. (5) 2, 745 (1935).
and enough 50 per cent sulfuric acid (about 200 cc.) is added, with stirring and cooling, to make the solution acid to Congo red paper. When the solution has cooled, it is extracted with eight 40fccc. portions of ether (Note 4). The ether extract is carefully distilled on a steam bath until the ether and chloroform are removed. ’
The residue is then placed in a modified Claisen flask (Org. Syn. 22, 11) and distilled under reduced pressure. Dimethyl-acrylic acid distils at 100-106°/20 mm. The yield of white solid is 49-53 g. (49-53 per cent of the theoretical amount). This product melts at 60-65°. It may be further purified by recrystallization from petroleum ether (b.p., 60-70°) or water (Note 5).