Polymerization, acetaldehyde

Like formaldehyde, acetaldehyde easily forms polymers, in this case paraldehyde and metaldehyde. Paraldehyde will form when hydrochloric or sulfuric acid is added to acetaldehyde. Polymerization of acetaldehyde to mec-aldehyde occurs in the gaseous phase in the presence of aluminum oxide or silicon dioxide catalyst. 

In the author s laboratories the polymerization of aldehydes, ketones, and alcohols by liquid hydrogen fluoride has been repeatedly noted. Acetaldehyde polymerizes and acetone forms polymeric substances on standing for a period of time in solution in hydrogen fluoride. If the solution is separated shortly after mixing, the acetone may be recovered. The same is true of tertiary alcohols. The peculiar action of tertiary chlorides (Simons et al., 35) probably results at least in part from polymerization. The products obtained most likely come from destruction of the polymers in the process of distillation. Benzaldehyde forms a shellac like resin when treated with hydrogen fluoride. A rather interesting polymerization reaction occurs upon treating aralkyl ketones with... 

Progress in the polymerization of the carbonyl linkage did not result until there was an understanding of the effect of ceiling temperature (Tc) on polymerization (Sec. 3-9c). With the major exception of formaldehyde and one or two other aldehydes, carbonyl monomers have low ceiling temperatures (Table 5-13). Most carbonyl monomers have ceiling temperatures at or appreciably below room temperature. The low Tc values for carbonyl polymerizations are due primarily to the AH factor. The entropy of polymerization of the carbonyl double bond in aldehydes is approximately the same as that for the alkene double bond. The enthalpy of polymerization for the carbonyl double bond, however, is appreciably lower. Thus AH for acetaldehyde polymerization is only about 29 kJ mol-1 compared to the usual 80-90 kJ mol-1 for polymerization of the carbon-carbon double bond (Table 3-14) [Hashimoto et al., 1076, 1978],... 

Fujii,H, Tsukuma, ., Saegusa,T, Furukawa,J. Initiation mechanism of acetaldehyde polymerization by alkyl aluminum catalyst Makromol. Chem. 82,32(1965). 

Ethanal (acetaldehyde) polymerizes under the influence of acids to the cyclic trimer, paraldehyde, and a cyclic tetramer, metaldehyde. Paraldehyde has been used as a relatively nontoxic sleep-producing drug (hypnotic). Metaldehyde is used as a poison for snails and slugs, Snarol. Ketones do not appear to form stable polymers like those of aldehydes. 

The first, and perhaps most vivid, example is the effect of the structure of a monomer crystal on polymerization in the solid state. The fact that the configuration of the emerging polymer depends directly on the structure of the solid monomer is no longer doubted, having been proved for many cases. Thus, depending on its phase, acetaldehyde polymerizes... 

In order to obtain high polymers rather than the trimer paraldehyde, the acetaldehyde polymerization must be carried out at low temperatures, and a proper balance of initiator activity and choice of solvent must be maintained. With a reasonably active initiator, increasing the polymerization temperature or the polarity of the solvent favors trimerization over polymerization. 

The polyacetaldehyde thus prepared has the same properties and structure as Letort s polyacetaldehyde which was obtained by crystallization polymerization. This indicates that crystallization polymerization, the only previously known method of acetaldehyde polymerization, is only a special case of acid-initiated or cationic acetaldehyde polymerization. We feel that Letort s proposal (29) that the peroxide-induced acetaldehyde polymerization (crystallization polymerization) as a radical polymerization can now be reinterpreted in the following way The initiating species, which is prepared by reacting acetaldehyde with a controlled amount of oxygen, is obtained via a... 

The most widely used initiator systems for acetaldehyde polymerization contain aluminum alkyls and zinc alkyls modified with water, alcohols, and amines (14,15, 24, 25, 37, 39, 42, 44, 47). 

An important reaction is that of acetaldehyde polymerization (Saucier et al. 1997 Romero and Baker 2000). This reaction not only increases the colouring intensity, but also intensifies the blue coloration (od 620 nm) that is responsible for the mauve tones in wine. 

It should be mentioned that under acidic conditions higher aldehydes, especially acetaldehyde with H2SO4, undergo very readily cyclo-trimerization to paraldehyde at temperatures below 0°C a small amount of the cyclic tetramer, metaldehyde, is also formed. The reaction is very fast and is accompanied by a rapid rise of temperature. As a consequence of this, the cationic acetaldehyde polymerization to linear polymers must always be carried out under conditions to avoid the trimerization using solvents of low dielectric constant, very low temperatures and initiators of appropriate activity. High dielectric constant solvents, high temperature, and very active initiators cause exclusively trimer formation. 

The kinetics of cationic polymerization of acetaldehyde or higher aldehydes in solution are even less understood. No rate data on acetaldehyde polymerization with BF3 in ether are available [6]. It is only known that after an induction period of 5—15 min a vigorous polymerization occurs which is completed in a few minutes. No attempts were made to control the temperature during this uncontrolled reaction and polymer precipitated. Other cationic polymerizations of acetaldehyde with less... 

The literature of aldehyde polymerization, particularly acetaldehyde polymerization, with modified aluminium alkyls as initiators is voluminous. The earliest studies were done by Ishida [60]. He found that there were remarkable differences in polymerization rate behaviour when the... 

Retardation and Inhibition. In order to obtain additional information on the polymerization process, various potential inhibitors or retarding agents were added to carbon suboxide, and the rate of polymer deposition from the gas phase was quantitatively studied at 100°C. To the monomer at a pressure of 330 mm Hg was added either an equimolar quantity of inhibitor based on pressure measurements, or room temperature vapor pressure of additive if less than 330 mm Hg. The additives used were oxygen, nitric oxide, 3-methyl-1-butene, 1,3-butadiene, acetone and acetaldehyde. Polymerization rates were followed by ESR measurements. 

Acetaldehyde, polymerized Acetaldehyde, polymers. See Metaldehyde Acetaldehyde, tetramer CAS 108-62-3 EINECS/ELINCS 202-945-6 UN 1332 (DOT)... 

Synonyms Acetaldehyde, homopolymer Acetaldehyde, polymerized Acetaldehyde, polymers META Metacetaldehyde Polyacetaldehyde 2,4,6,8-Tetramethyl-1,3,5,7-tetraoxacyclooctane or acetaldehyde homopolymer... 

In principle, other double bonds should also be polymerizable. Trifluoro-acetaldehyde polymerizes free radically since the substituent is electron attracting and the macroradical formed is thereby stabilized ... 

---