Preparation of Acetaldehyde

Introduction. Acetaldehyde, CHsCHO, polymerizes easily to paraldehyde, (CH3CHO)8. In the presence of a catalyst, such as sulfuric acid, the polymerization proceeds rapidly. The reaction is reversible and may be represented by the following equation  

For polsunerization, acetaldehyde is cooled and a small amount of sulfuric acid is added. Since paraldehyde is not soluble in water and acetaldehyde dissolves readily, the polymerized mixture is washed with water to remove the catalyst and any unchanged monomer. In the pure form, paraldehyde keeps well. When acetaldehyde is needed, a few drops of sulfuric acid are added to paraldehyde, and the mixture heated in a flask to which is attached a fractionating column connected with a condenser and receiver. The receiver is cooled in a freezing mixture. The application of heat in the presence of a catalyst reverses the polymerization and aldehyde is formed. 

Very slowly. The temperature in the fractionating column is not allowed to rise much above room temperature, and therefore any paraldehyde that boils off with the acetaldehyde condenses and falls back into the flask. When the distillation is complete, note whether any liquid is left in the flask. The acetaldehyde is kept at a temperature of 5-10°, and used as required. 

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An alkyne is a hydrocarbon that contains a carbon-carbon triple bond. Acetylene.. H—C= C—H, the simplest alkyne, was once widely used in industry as the starting material for the preparation of acetaldehyde, acetic acid, vinyl chloride, and other high-volume chemicals, but more efficient routes to these substances using ethylene as starting material are now available. Acetylene is still used in the preparation of acrylic polymers but is probably best known as the gas burned in high-temperature oxy-acetylene welding torches. 

Substances having triple linkages when dissolved in sulphuric acid take up the elements of water, particularly if mercuric salts are present. The simplest example of this reaction is the preparation of acetaldehyde from acetylene itself in the manner described above. 

A) Preparation of Acetaldehyde (Sm.). Arrange apparatus as shown in Figure 33. Place 6 ml of paraldehyde in an eight-inch distilling tube. Add two boiling stones and 5 drops of concentrated sulfuric acid, and connect with the receiving tube. Immerse the latter in an ice-salt mixture. Heat by means of a very small smoky flame so that the temperature as indicated by the thermometer does not rise above 21°. Discontinue the distillation when the residue is about 0.5 ml. Place the aldehyde in an icebox and use it as needed. 

B) Preparation of Acetaldehyde (M.). Use a flask fitted with a fractionating colunm or a distilling flask having a Vigreau column. Place in the flask 100 ml of paraldehyde, 1 ml of concentrated sulfuric acid, and two boiling stones. Connect with a condenser fitted with an adapter which leads to a receiver surrounded by a freezing mixture. Place a small luminous flame under the flask and heat... 

A patent, the specifications of which are very hroad, describes the preparation of acetaldehyde and also of various other substances by the... 

The preparation of acetaldehyde diethyl acetal in 65% yield by use of calcium chloride and hydrochloric acid as catalysts is described in Organic Syntheses.909... 

With the best preparation of acetaldehyde-sulfonate available, which according to analysis was 70% pure, the effect of pH on dissociation was determined. The results obtained, rhown as curve 3 in Fig. 3, indicate the... 

When one is discussing oxidation of olefins with dual metal catalysts it is difficult to avoid the subject of the Wacker reaction. This extremely important synthetic method using various mixtures of metal salts (Pd/Cu, Pd/Fe, Rh/Fe, etc.) allows the preparation of acetaldehyde or vinyl acetate from ethylene equations (1) and (2), as well as many other useful synthetic procedures. Reactions (1) and (2) occur, however, via nucleophilic attack of coordinated water or acetate, equations (319)-(321), followed by j3-hydrogen elimination. 

Aldehydes and ketones may also be produced by the hydration of alkynes. If the triple bond is on the last carbon in a carbon atom chain, an aldehyde is produced if the bond is between internal carbons, the result is a ketone. A typical reaction is the commercial preparation of acetaldehyde ... 

The procedure used for the preparation of [l,2- C2]acetic acid is closely related to that described above for the preparation of acetaldehyde. In this case, however, the Hg(II)-... 

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