2.2- dimethyl-2- -acetaldehyde

Acetals and Acylals. Acetals, which contain the group >C(OR)2, where R may be different, are named (1) as dialkoxy compounds or (2) by the name of the corresponding aldehyde or ketone followed by the name of the hydrocarbon radical(s) followed by the word acetal. For example, CH3—CH(0CH3)2 is named either (1) 1,1-dimethoxyethane or (2) acetaldehyde dimethyl acetal. 

Several of the lower molecular weight aliphatic compounds, in a mixture, are part of the roasted coffee aroma. A nine-compound mixture with roasted coffee aroma contained isopentane, n-hexane, acetaldehyde, dimethyl sulfide, propanal, isobutanal, isopentanal, methanol, and 2-methylfuran.20 In addition, the freshness of aroma and taste has been correlated with 2-methylpropanal and diacetyl. When the concentration of these falls off, so does the taste.21 Other aliphatic compounds that are steadily lost from ground roasted coffee, unless it is vacuum packaged, include methyl formate, methyl acetate, methyl thioacetate, and acetone.22 The concentrations in roast coffee for four compounds whose contribution to the fresh flavor have long been known are dimethyl sulfide (4 ppm), methyl formate (12 ppm), isobutanal (20 ppm), and diacetyl (40 ppm). The taste thresholds are 0.1, 0.5, 0.5, and 1.0 ppm, respectively, in the brew made with 5 g coffee per 100 ml water.15... 

Acetaldehyde ammonia, al62 Acetaldehyde diethyl acetal, d303 Acetaldehyde dimethyl acetal, d504... 

B. (4R,5S)-3-(1-Methoxyethyl)-4,5-diphenyl-2-oxazolidinone. A 2-L, threenecked, round-bottomed flask equipped with a magnetic stirrer, thermometer, and a reflux condenser is charged with (4R,5S)-4,5-diphenyl-2-oxazolidinone (20.0 g, 84 mmol), ( )-10-camphorsulfonic acid (9.7 g, 42 mmol) (Note 7), and acetaldehyde dimethyl acetal (700 mL) (Note 8). The mixture is heated at gentle reflux in an oil bath (bath temperature 80°C) for 5 hr (Note 9). The mixture is allowed to cool to ambient temperature, then concentrated under reduced pressure on a rotary evaporator (Note 10). Ethyl acetate (100 mL) is added to the residue, and the ethyl acetate solution is transferred to a beaker. The solution is neutralized with saturated sodium bicarbonate solution (100 mL) (Note 11), and transferred into a separatory funnel. The two layers are separated, and the lower aqueous layer is extracted with ethyl acetate (100 mL). 

Acetaldehyde dimethyl acetal was purchased from Tokyo Kasei Kogyo Co., Ltd. It is also available from Aldrich Chemical Company, Inc. 

Excess acetaldehyde dimethyl acetal can be recovered by distillation. 

Methanolysis of 9-(l-methoxyethyl)carbazole with methanol-hydrogen chloride gave carbazole and acetaldehyde dimethyl acetal. 9,9 -Di-(3,6-dibromocarbazolyl)methane gave 9-acetyl-3,6-dibromocarbazole with acetic anhydride and a trace of sulfuric add. ... 

Acetaldehyde dimethyl acetal [534-15-6] M 90.1, b 63-65°, dj0 0.852, n 51.36678. Distd through a fractionating column and fraction boiling at 63.8°/751mm is collected. It forms an azeotrope with MeOH. 

The synthesis of benzo[6]thiophenes by the PPA-promoted cyclization of (arylthio)acetaldehyde dimethyl or diethyl acetals [Eq. (4)] was introduced by Tilak287, 288 in 1950 and improved in 1951.289 The acetals are readily prepared from aryl mercaptans and bromo-acetaldehyde dimethyl (or diethyl) acetal in the presence of sodium ethoxide, or by reaction of an aryllithium compound with [(MeO)2CHCH2S]2.290 Diethyl acetal as starting material sometimes gives better yields of product than the corresponding dimethyl acetal.291 Optimum yields of benzo[6]thiophenes are obtained when cyclization of the acetals is carried out under reduced pressure so that the lower boiling benzo[6]thiophenes distill as soon as they are formed. Experimental conditions for obtaining optimum yields vary from case... 

The PPA-promoted cyclizations of (phenylthio)acetaldehyde dimethyl acetal and a-(phenylthio)propionaldehyde diethyl acetal yield benzo[6]thiophene together with 3-methoxy-2,3-dihydrobenzo-[6]thiophene, and a mixture of 2- and 3-methylbenzo[6]thiophene, respectively.296 Mechanisms have been proposed to account for these results. 

Nitrobenzo[6]thiophene is obtained in 10% yield by the cycliza-tion of (p-nitrophenylthio)acetaldehyde dimethyl acetal (Section IV,B) 7-nitrobenzo[6]thiophene cannot be prepared by this method.488 5-Nitrobenzo[6]thiophene84,218,338,422,538,543-545 and its 3-phenyl,333 3-methyl,298 3,6-dimethyl,330 and 7-nitro-3-phenyl334 derivatives may be obtained most conveniently by decarboxylation of the readily available (Section IV, D) 2-carboxylic acids. 5- 4 J4.54e 0. 494,548 an(j 7.494 nitro-3-acetoxybenzo[6]thiophene may be prepared almost quantitatively by cyclization reactions (Section IV, D). 

Hydroxybenzo[6]thiophene has been isolated from coal tar.42 It may be prepared from 6-aminobenzo[fr]thiophene by standard procedures.241 6-Methoxybenzo[h]thiophene may be prepared by decarboxylation of the corresponding 2-carboxylic acid,341 and 6-ethoxybenzo[6]thiophene is obtained by reduction of 6-(ethoxy)-thioindoxyl (Section VI, 1,2). 6-Methoxy-5-methylbenzo[6]thiophene is obtained by cyclization of (3-methoxy-4-methylphenylthio)-acetaldehyde dimethyl acetal (Section IV,B).617 The product previously described542 as 6-hydroxy-3-phenylbenzo[6]thiophene has now been shown to be the 2-phenyl isomer.307 6-Methoxy-818 and 6-methoxy-5-methyl-benzo[6]thiophene617 are demethylated by pyridine hydrochloride. 

Methoxybenzo[6]thiophene may be prepared by cyclodehydration of (o-methoxyphenylthio)acetaldehyde dimethyl acetal (Section... 

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