Polymerisation of Aldehydes

Furukawa et al. [274] and Natta cl al. [275,276] succeeded independently in the preparation of crystalline polyacetaldehyde by using some organometallic compounds, such as diethylzinc or triethylaluminium, for the low-temperature polymerisation of acetaldehyde. Metal alkyls and metal alkoxides, e.g. aluminium isopropoxide, zinc ethoxide or ethyl orthotitanate, have also polymerised other aldehydes such as propionaldehyde and trichloroacetaldehyde to give crystalline polymers (Table 9.3) [270,275,277], A highly crystalline isotactic polymer has been obtained from the polymerisation of w-butyraldehyde with triethylaluminium or titanium tetrachloride-triethylaluminium (1 3) catalysts. Combinations of metal alkyl, e.g. diethylzinc, with water [278] or amine [279] appeared to give very efficient catalysts for aldehyde polymerisations. 

The formation of a complex between the carbonyl oxygen atom of the aldehyde monomer and the catalyst metal atom, followed by its rearrangement to the respective metal alkoxide of secondary alcohol, has been suggested to be the first polymerisation step [274,277,280,281], In the case of alumina as a catalyst, the aldehyde coordination was confirmed by IR spectroscopy [282], 

On the basis of studies of the reactions of formaldehyde, acetaldehyde and butyraldehyde with ethylzinc diphenylamide as a model catalyst of moderate effectiveness, Van der Kerk [279] revealed the mechanism of aldehyde coordination polymerisation by means of organozinc catalysts  

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J. Eumkawa and T. Saegusa, Polymerisation of Aldehydes and Oxides-, Wdey-Interscience, New York, 1963. 

Care has to be taken in the polymerisation of aldehyde polymers in order to achieve reproducible results. It is also difficult to stabilise most of the products since thermodynamics frequently favour depolymerisation at temperatures a little above or at room temperature. 

These reversible polymerisations of aldehydes are to be distinguished from the condensations which they can also undergo. Thus formaldehyde is converted by quite weak alkalis (Ca(OH)2, CaC03) into glycollic aldehyde and glyceraldehyde, and further into a mixture of hexoses (Butlerow, 0. Loew) from which E. Fischer isolated the so-called... 

DAVIDSON, R. L., and SITTIG, M., Water Soluble Resins, Reinhold, New York (1%2) furukawa, and saegusa, t Polymerisation of Aldehydes and Oxides, Interscience, New York (1963). 

Acetaldehyde is a highly reactive compound exhibiting the general reactivity of aldehydes (qv). Acetaldehyde undergoes numerous condensation, addition, and polymerisation reactions under suitable conditions, the oxygen or any of the hydrogens can be replaced. 

Add a drop or two of concentrated sulphuiic acid to I c.c. of aldehyde. The mixture becomes hot in consequence of the aldehyde undergoing polymerisation to paraldehyde... 

A bacterial isolate APN has been shown to convert a-aminopropionitril enantioselectively to L-alanine (94% yield, 75% e e). However, the major disadvantage of this approach, is the low stability of most aminonitriles in water (for example a-aminophenylacetonitrile in water of pH 7, degrades completely within 48 hours). The aminonitriles are always in equilibrium with the aldehyde or ketone and ammonia/HCN. Polymerisation of hydrogen cyanide gives an equilibrium shift resulting in the loss of the aminonitrile. Therefore, a low yield in amino adds is to be expected, which makes this method less attractive for the industrial synthesis of optically active amino adds. 

A store of 250 m of acrolein detonated. This was probably due to the spontaneous polymerisation of the aldehyde. 

Pyruvic acid is not stable at ambient temperature when it is stored for a long period of time. It can only be stored in a refrigerated room. A bottle of this acid was stored in a laboratory at 25°C and detonated, probably because of the overpressure created by the formation of carbon dioxide. Indeed, with diacids and complex acids the decomposition is made by decarboxylation. In this particular case, this decomposition should give rise to acetaldehyde. It could be asked whether, in the exothermic conditions of this decomposition, a polymerisation of this aldehyde (see Aldehydes-ketones on p.310) did not make the situation worse. 

It is marketed as a 35-40 per cent, solution in water (formalin). The rpactions of formaldehyde are partly typical of aldehydes and partly peculiar to itself. By evaporating an aqueous solution paraformaldehyde or paraform (CH O), an amorphous white solid is produced it is insoluble in most solvents. When formaldehyde is distilled from a 60 ptr cent, solution containing 2 per cent, of sulphuric acid, it polymerises to a crystalline trimeride, trioxane, which can be extracted with methylene chloride this is crystalline (m.p. 62°, b.p. 115°), readily soluble in water, alcohol and ether, and devoid of aldehydic properties ... 

Many years later, Schwartz (Schwartz and Goverde, 1982 Voet and Schwartz, 1983) discovered that the synthesis of adenine via polymerisation of HCN can be accelerated by adding formaldehyde and other aldehydes. Reactions in the gas phase (nitrogen/methane atmosphere) promoted by electrical discharges led to the formation of cyanoacetylene in relatively good yields the latter reacts with urea to give various products, including cytosine (Sanchez et al., 1968). 

The coordination polymerisation of heterounsaturated monomers, such as aldehydes [101-103] and ketones [104], isocyanates [105] and ketenes [106,107], in homopolymerisation systems has not been widely described in the literature. However, the coordination copolymerisation of heterounsaturated monomers not susceptible to homopropagation, such as carbon dioxide [71,108-113], with heterounsaturated monomers such as cyclic ethers has been successfully carried out and is of increasing interest. 

Heterounsaturated monomers such as aldehydes or carbon dioxide polymerise and/or copolymerise with the participation of at least two metal atoms in multicentred transition states. Scheme (9) shows the initiation and propagation steps in the coordination polymerisation of carbonyl monomers with catalysts containing an Mt-X active bond [125] ... 

Several papers have appeared in the literature in recent years showing that certain metal acetylacetonates can function as initiators for the polymerisation of vinyl and diene monomers in bulk and solution (1 - 12). Results for the kinetics of bulk and solution polymerisation are consistent with the view that the reaction occurs by a free-radical mechanism. The usual free-radical kinetics are operative, but an unusual feature is that, in some cases, certain additives such as chlorinated hydrocarbons have an activating effect upon the reaction by inducing more rapid decomposition of the initiator (2,11,12,13). Other additives which have been reported as promotors for the polymerisation include pyridlne(14) and aldehydes and ketones(15). The complexity of the reaction in the presence of such additives is evident from the fact that chloroform has been reported to be an inhibitor for the poly-merlsatlon(3). 

Auld and Hantzsch, from acetaldehyde and mercuric oxide in slightly alkaline solution, obtained a base, trimercuridialdehyde hydroxide, which readily polymerised to a white powder, (CJTgOgHgg), . The latter decomposes without znelting at about 100° C, and is insoluble in the usual organic solvents, decomposed by dilute hydrochloric acid with formation of acetaldehyde and mercuric chloride, but not affected by dilate acetic acid. The investigators state that this is a delicate test for the presence of small quantities of acetaldehyde, since it detects the presence of one part of aldehyde in 6000 parts of water. ... 

The application of organometallic compounds in medicine, pharmacy, agriculture and industry requires the accurate determination of these metals as part of their application. Most % complexes characterised by direct carbon-to-carbon metal bonding may be classified as organometallic and the nature and characteristics of the n ligands are similar to those in the coordination metal-ligand complexes. The -complex metals are the least satisfactorily described by crystal field theory (CFT) or valence bond theory (VBT). They are better treated by molecular orbital theory (MOT) and ligand field theory (LFT). There are several uses of metal 7i-complexes and metal catalysed reactions that proceed via substrate metal rc-complex intermediate. Examples of these are the polymerisation of ethylene and the hydration of olefins to form aldehydes as in the Wacker process of air oxidation of ethylene to produce acetaldehyde. 

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