Acetal acetaldehyde diethylacetal

Place 50 g. of anhydrous calcium chloride and 260 g. (323 ml.) of rectified spirit (95 per cent, ethyl alcohol) in a 1-litre narrow neck bottle, and cool the mixture to 8° or below by immersion in ice water. Introduce slowly 125 g. (155 ml.) of freshly distilled acetaldehyde, b.p. 20-22° (Section 111,65) down the sides of the bottle so that it forms a layer on the alcoholic solution. Close the bottle with a tightly fitting cork and shake vigorously for 3-4 minutes a considerable rise in temperature occurs so that the stopper must be held well down to prevent the volatilisation of the acetaldehyde. Allow the stoppered bottle to stand for 24-30 hours with intermittent shaking. (After 1-2 hours the mixture separates into two layers.) Separate the upper layer ca. 320 g.) and wash it three times with 80 ml. portions of water. Dry for several hours over 6 g. of anhydrous potassium carbonate and fractionate with an efficient column (compare Section 11,17). Collect the fraction, b.p. 101-104°, as pure acetal. The yield is 200 g. 

Acetals are usually liquid they are almost unaffected by alkalis and are not attacked by metallic sodium nor by Fehling s solution. They are identified by reference to the alcohol and aldehyde (or ketone if a ketal) which they yield when hydrolysed in acid solution. Hydrolysis proceeds readily in dilute acid solution e.g., with 3-5 per cent, acid).  

The rate of hydrolysis depends upon the solubUity of the acetal m the hydrolysis medium. Acetals of low molecular weight are completely hydrolysed by refluxing for 5-10 minutes those of higher molecular weight, and therefore of small solubility, may require 30-60 minutes, but 

CAUTION. Acetals, like ethers, may contain explosive peroxides which must be removed before distillation is attempted. The procedure to be adopted is similar to that described under Ethers (see Section 111,60). 

The experimental procedure to be followed depends upon the products of hydrolysis. If the alcohol and aldehyde are both soluble in water, the reaction product is divided into two parts. One portion is used for the characterisation of the aldehyde by the preparation of a suitable derivative e.g., the 2 4-dinitrophenylhydrazone, semicarbazone or di-medone compound—see Sections 111,70 and 111,74). The other portion is employed for the preparation of a 3 5-dinitrobenzoate, etc. (see Section 111,27) it is advisable first to concentrate the alcohol by dis tillation or to attempt to salt out the alcohol by the addition of solid potassium carbonate. If one of the hydrolysis products is insoluble in the reaction mixture, it is separated and characterised. If both the aldehyde and the alcohol are insoluble, they are removed from the aqueous layer separation is generally most simply effected with sodium bisulphite solution (compare Section Ill,74),but fractional distillation may sometimes be employed. 

---

Acetal (acetaldehyde diethylacetal) [ 105-57-7] M 118.2, b 103.7-104 , d 0.831, n 1.38054, 1.3682. Dried over Na to remove alcohols and water, and to polymerise aldehydes, then fractionally distd. Or, treat with alkaline H2O2 soln at 40-45° to remove aldehydes, then the soln is saturated with NaCl, separated, dried with K2CO3 and distd from Na [Vogel J Chem Soc 616 1948]. 

Fig. 21. Hydrolysis of acetals at 20°C on a Dowex 50W X10 resin catalyst [513]. Rate coefficients of the resin-catalysed reaction (feres) versus rate coefficients of the reaction catalysed by dissolved inorganic acid (fehom)- 1 Formaldehyde dimethylacetal 2, formaldehyde diethylacetal 3, formaldehyde di-2-propylacetal 4, acetaldehyde ethyleneacetal 5, acetone ethyleneacetal 6, acetaldehyde dimethylacetal 7, acetaldehyde diethylacetal. The slope for acetals 1—3 is 1, for the acetals 3—7 0.5.

Ni-TMiBC (110) was obtained from pyrrole and acetaldehyde diethylacetal in an acetic acid solution of Ni(II) acetate under an inert atmosphere in a yield of about 1% based on Ni (84JA5164). 

Hemiacetals, such as acetaldehyde, diethylacetal and citral dimethyl acetal... 

Beilstein Handbook Reference) Acetaal Acetal Acetal diethylique Acetaldehyde diethyl acetal Acetaldehyde ethyl acetal Ace Acetol Aceton NS Acetron GP AI3-24135 AT-20GF BRN 1098310 Oiaethylacetal 1,1-Diaethoxy-aethan 1,1-Diathoxy-athan 1,1-Diethoxy-elhaan 1,1-Diethoxyethane Diethyl acetal Diethylacetal 1.1-Dletossietano EINECS 203-310-6 Ethane,... 

Hydrogen sulfide and aliphatic and aromatic thiols react readily with [ C]nitriles to give [ C]thioamides in yields of 45-70%. Upon treatment with a-halocarbonyl compounds they form [ C]thiazoles (Hantzsch thiazole synthesis). This was exploited for the synthesis of 2-(4-chlorophenyl)[2- C]thiazol-4-acetic acid f89. X = COOH) (Figure 7.23) and the 2-(2-phthalimidoethyl)-[2- C]tliiazole derivative 91 °. which were obtained when the corresponding thioamides M and 90 were treated with 1,3-dichloroacetone and bromo-acetaldehyde diethylacetal, respectively. As illustrated by the third example in Figure 7.23,... 

The 2-thiobenzoyl acetaldehyde diethyl acetal (17.2 g) was dissolved in 100 ml THF followed by the addition of 6 g NaOH in 20 ml H20. The mixture was refluxed under N2 for 15 h, then cooled and diluted with water (200 ml) and the product extracted with ether (3 x 200 ml). The extract was dried, the solvent removed in vacuo and the residue distilled to yield 7.1 g of mercaptoacetaldehyde diethylacetal. 

The smaller TON (calculated for ethylbenzene oxidation) and the lower conversion in ethanol is due to the oxidation of the solvent itself, as already reported [18]. The main product of ethanol oxidation is diethylacetal formed by initial oxidation of the alcohol to acetaldehyde and further nucleophilic addition and substitution with other alcohol molecules. Some amount of acetic acid and acetaldehyde are also observed in the reaction mixture. However, the... 

---