Paraldehyde and acetaldehyde

Polymerization. Paraldehyde, 2,4,6-trimethyl-1,3-5-trioxane [123-63-7] a cycHc trimer of acetaldehyde, is formed when a mineral acid, such as sulfuric, phosphoric, or hydrochloric acid, is added to acetaldehyde (45). Paraldehyde can also be formed continuously by feeding Hquid acetaldehyde at 15—20°C over an acid ion-exchange resin (46). Depolymerization of paraldehyde occurs in the presence of acid catalysts (47) after neutralization with sodium acetate, acetaldehyde and paraldehyde are recovered by distillation. Paraldehyde is a colorless Hquid, boiling at 125.35°C at 101 kPa (1 atm). 

Depolymerization of paraldehyde occurs in the presence of acid catalysts, and, after neutralization with sodium acetate, acetaldehyde and paraldehyde are recovered by distillation. 

Acetaldehyde and Paraldehyde.— As a second example of the equilibria between two isomerides, we shall take the two isomeric (polymeric) forms of acetaldehyde, which have been exhaustively studied. ... 

Tautomers consist of an intimate mixture of different species of molecules (metamers or polymers) in statistical equilibrium with one another and inseparable under ordinary experimental conditions. This includes the case of water, where the distinction between one substance covering many species in equifibrimn (and their variation as a function of pressure and temperature) is quite clear. R also includes cases like the pseudobinary system acetaldehyde and paraldehyde. The two substances are stable and can be mixed in all proportions at low temperatures, forming solutions. But addition of traces of sulphuric acid catalyzes a mutual transformation and a stable equilibrium between the monomer and the trimer is established (at each temperature). Similarly, eth3me C2H2 and benzene CeHe are normally considered two different substances, but at higher temperature, in the presence of a catalyst, they behave as one component. 

Acetaldehyde, b.p. 21°, undergoes rapid pol5unerisation under the influence of a little sulphuric acid as catalyst to give the trimeride paraldehyde, a liquid b.p. 124°, which is sparingly soluble in water. The reaction is reversible, but attains equilibrium when the conversion is about 95 per cent, complete the unreacted acetaldehyde and the acid catalyst may be removed by washing with water ... 

Reactions with Ammonia and Amines. Acetaldehyde readily adds ammonia to form acetaldehyde—ammonia. Diethyl amine [109-87-7] is obtained when acetaldehyde is added to a saturated aqueous or alcohoHc solution of ammonia and the mixture is heated to 50—75°C in the presence of a nickel catalyst and hydrogen at 1.2 MPa (12 atm). Pyridine [110-86-1] and pyridine derivatives are made from paraldehyde and aqueous ammonia in the presence of a catalyst at elevated temperatures (62) acetaldehyde may also be used but the yields of pyridine are generally lower than when paraldehyde is the starting material. The vapor-phase reaction of formaldehyde, acetaldehyde, and ammonia at 360°C over oxide catalyst was studied a 49% yield of pyridine and picolines was obtained using an activated siHca—alumina catalyst (63). Brown polymers result when acetaldehyde reacts with ammonia or amines at a pH of 6—7 and temperature of 3—25°C (64). Primary amines and acetaldehyde condense to give Schiff bases CH2CH=NR. The Schiff base reverts to the starting materials in the presence of acids. 

A. ot-Chloroelhyl ethyl ether. A mixture of 200 g. (201 ml.) of redistilled paraldehyde, b.p. 121-122.5° (equivalent to 4.54 moles of acetaldehyde), and 200 g. (254 ml., 4.34 moles) of absolute ethanol is placed in a 1-1. three-necked flask fitted with a mechanical stirrer and a gas inlet tube reaching to the bottom of the flask. The mixture is cooled to —5° in a mixture of Dry Ice and acetone, and dry hydrogen chloride (Note 1) is passed into the stirred reaction mixture maintained at about —5° until 200 g. (5.48 moles) has been absorbed. During this operation, which requires about 2 hours, the reaction mixture separates into two layers. The upper layer of crude a-chloroethyl ethyl ether is re-... 

Tetrahydroharman, m.p. 179-80°, has been prepared by a number of workers by a modification of this reaction, viz., by the interaction of tryptamine (3-)5-aminoethylindole) with acetaldehyde or paraldehyde and Hahn et al. have obtained a series of derivatives of tetrahydronorharman by the use of other aldehydes and a-ketonic acids under biological conditions of pH and temperature, while Asahina and Osada, by the action of aromatic acid chlorides on the same amine, have prepared a series of amides from which the corresponding substituted dihydronorharmans have been made by effecting ring closure with phosphorus pentoxide in xylene solution. 

Paraldehyde Paraldehyde, 2,4,6-trimethyl-l,3,5-trioxane (4.3.2), is a trimeric acetaldehyde which is synthesized by the acid-catalyzed polymerization of acetaldehyde and at moderate and high temperatures [32,33]. 

In 1972, Eiter and his group reported the synthesis of a-alkoxy dialkyl N-nitrosamines (11),which can be obtained easily in 20-50 g quantities. This synthetic scheme works well when formaldehyde was used. In those cases when higher aliphatic aldehydes are used (e.g. acetaldehyde), the yields decreased to 3-5%. The a -alkoxy dialkyInitrosamines always contained the trimeric paraldehyde as impurity. When acetaldehyde and... 

Ethyl-3-methylpyridine (also known as aldehyde-collidine ) has been prepared by heating aldehyde-ammonia aldehyde-ammonia and acetaldehyde or paraldehyde aldol-ammonia and ammonia paraldehyde and ammonia <> 11,12 acetamide,1 or acetamide and phosphorus pentoxide ethylene glycol and ammonium chloride ethylidene chloride or bromide and ammonia ethylidene chloride and acetamide, ethylamine, or n-amylamine crotonic acid and a calcium chloride-ammonia complex 1 and by passage of acetylene or acetaldehyde and ammonia over alumina and other catalysts. 

The lowest-cost synthetic pyndine base, 2-mcthyl-5-cthylpyridinc, is made in a liquid-phase process from paraldehyde (derived from acetaldehyde) and aqueous ammonia 111 the presence of ammonium acetate at approximately 102- 190 atmospheres and 220-280cC in 70-80% yield. Minor byproducts include 2- and 4-picoline. 

Reaction LXXXH. Condensation of an Aldehyde with itself under the Action of Mineral Acids or of Calcium Chloride. (A., 27, 319 162, 143 203, 26, 43.)—If acetaldehyde is treated with calcium chloride or mineral acids, such as cone, sulphuric acid or gaseous hydrogen chloride, polymerisation occurs and paraldehyde is formed. A certain amount of metaldehyde is also obtained its quantity increases with reduction in the temperature of polymerisation. 

Given in the literature are vapor pressure data for acetaldehyde and its aqueous solutions (1—3) vapor—liquid equilibria data for acetaldehyde—ethylene oxide [75-21-8] (1), acetaldehyde—methanol [67-56-1] (4), sulfur dioxide [7446-09-5]— acetaldehyde—water (5), acetaldehyde—water—methanol (6) the azeotropes of acetaldehyde—butane [106-97-8] and acetaldehyde—ethyl ether (7) solubility data for acetaldehyde—water—methane [74-82-8] (8), acetaldehyde—methane (9) densities and refractive indexes of acetaldehyde for temperatures 0—20°C (2) compressibility and viscosity at high pressure (10) thermodynamic data (11—13) pressure—enthalpy diagram for acetaldehyde (14) specific gravities of acetaldehyde—paraldehyde and acetaldehyde—acetaldol mixtures at 20/20°C vs composition (7) boiling point vs composition of acetaldehyde—water at 101.3 kPa (1 atm) and integral heat of solution of acetaldehyde in water at 11°C (7). 

Toxicity. The minimum lethal dose has been estimated as 25 ml orally and 12 ml rectally, although recovery has occurred after the ingestion of 125 ml. Toxic effects have been associated with blood concentrations of 200 to 400 pg/ml. Blood concentrations of about 500 pg/ml, or less if alcohol has also been ingested, may be lethal. On storage, paraldehyde may depolymerise to acetaldehyde and acetic acid severe acidosis and fatalities may follow the use of partly depolymerised material. 

Thus acetone, acetaldehyde, and esters condense to dimers in the first stage. From aldehydes we also can obtain six-membered rings such as trioxane from CU2O, paraldehyde from CHaCHO, etc. Dienes often give dimers reversibly. 

From Acetaldehyde and Malonic Acid.—Another synthesis proves the constitution of crotonic acid as A2-butenoic acid. A di-basic acid known as malonic acid has the constitution of di-carhoxy methane HOOC—CH2—COOH. When this acid is heated with acetaldehyde (paraldehyde) and glacial acetic acid condensation occurs as in the synthesis of crotonic aldehyde and in the Perkin-Fittig synthesis (p. 172). A dibasic acid is obtained which loses carbon dioxide and yields a mono-basic acid which is crotonic acid. 

Paraldehyde is metabolized in the liver to acetaldehyde (22), and the metabohsm of aldehyde by aldehyde dehydrogenase is inhibited by disulfiram, causing aldehyde toxicity. The adverse effects of this have been shown in experimental animals (23) and there have been reports of confusional psychosis in patients given disulfiram and paraldehyde (24). 

The kinetics of the Witten oxidation process are complicated by the presence of several possible radical chain carrying steps and termination steps.A full treatment of these kinetics has not been published. What is known about the kinetics is that the initial oxidation of p-xylene to p-toluie acid is inversely proportional to [Co ], an induction period generally attributed to the oxidation of Co to Co is observed, the rate of conversion of p-xylene to p-toluic acid is faster than that of methyl p-toluate to monomethyl terephthalate, and the rate of the first oxidation step (and not the second) can be greatly increased by the addition of radical sources, such as acetaldehyde or paraldehyde. 

The roles of manganese in TPA manufacture are better understood than in the Witten process, and include decomposition of the CH2COOH radical (derived from the acetic acid solvent) and regeneration of the bromine atom promoter [13], In an effort to eliminate halogen compounds which are highly corrosive to oxidation equipment, use of acetaldehyde [14] and paraldehyde [15] has been developed. These aldehyde promoters are ultimately converted to acetic acid in high yield. For economic reasons, these aldehyde processes have been abandoned in favor of the bromine-promoted Amoco process. 

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