Hydroxy acids diacids

Formation of a polyfunctional organomagnesium reagent useful in the synthesis of p-hydroxy acids, diacids. 

Hie most representative member of this class of polyesters is the low-molar-mass (M 1000-3000) hydroxy-terminated aliphatic poly(2,2/-oxydiethylene adipate) obtained by esterification between adipic acid and diethylene glycol. This oligomer is used as a macromonomer in the synthesis of polyurethane elastomers and flexible foams by reaction with diisocyanates (see Chapter 5). Hydroxy-terminated poly(f -caprolactonc) and copolyesters of various diols or polyols and diacids, such as o-phthalic acid or hydroxy acids, broaden the range of properties and applications of polyester polyols. 

The carboxy-hydroxy reaction (direct esterification) is the most straightforward method of polyester synthesis. It was first reported in the 1930s by Carothers10 12 and is still a very widely used method for the synthesis of polyesters from diacids and diols (Scheme 2.12) or from hydroxy acids (Scheme 2.13). Direct... 

Polyesters have been obtained in organic medium by polyesterification of hydroxy acids,328,329 hydroxy esters,330 stoichiometric mixtures of diols and diacids,331-333 diols and diesters,334-339 and diols and cyclic anhydrides.340 Lipases have also been reported to catalyze ester-ester interchanges in solution or in die bulk at moderate temperature.341 Since lipases obviously catalyze the reverse reaction (i.e., hydrolysis or alcoholysis of polyester), lipase-catalyzed polyesterifications can be regarded as equilibrium polycondensations taking place in mild conditions (Scheme 2.35). 

The reaction mixture at any instance consists of various-sized diol, diacid, and hydroxy acid molecules. Any HO-containing molecule can react with any COOH-containing molecule. This is a general characteristic of step polymerization. 

For many step polymerizations there are different combinations of reactants that can be employed to produce the same type of polymer (Table 1-1). Thus the polymerization of a hydroxy acid yields a polymer very similar to (but not the same as) that obtained by reacting a diol and diacid ... 

Compared to the anodic oxidation of Z-4-octene-l,8-diol (80%, Table 8) its oxidation with pyridinium dichromate in dimethyl formamide gave as the best chemical alternative only 65 % diacid Nickel peroxide oxidation under mild conditions (1.3 eq. peroxide, 25 °C, 1 M NaOH) led to 45% hydroxy acid 75, whereas under more vigorous conditions (3 eq. peroxide, 80 °C, 1 M NaOH) maleic acid was formed ... 

Other preparations of 2-iminothiazolidin-4-ones which are discussed in the review by Brown139 utilize the reactions of thiourea with a-hydroxy acids,146 ethyl diazoacetate,73 glycidic esters,74,147 cinnamic acid,148 unsaturated diacids (fumaric, maleic, and citraconic) or their esters or imides,149-152 and propiolic esters.153,154 There has been considerable controversy in the literature surrounding the propiolic ester synthesis since many workers have proposed that the products are 1,3-thiazines (see Section IV, B, 1). The pertinent papers in this controversy have been summarized by Cain and Warrener.155 Nagase158 has recently settled the argument in favor of the 2-iminothiazolidin-4-... 

Polymer synthesis by step-reaction involves the coupling of small molecules which are difunctional by virtue of having two reactive functional groups. It is common for the coupling to involve elimination of a small molecule, and typical examples might be the synthesis of a polyester from a hydroxy-acid or of a polyamide by reaction of a diamine with a diacid. Step-reaction polymerizations are often equilibria, whereas chain-reaction polymerizations are more usually irreversible. 

Several 21,22-seco-diacids (150) have been prepared in the 20/S,28-epoxy-18a,19/8H-ursane series by oxidation of the corresponding 22-hydroxymethylene-21-ketones (151). Reaction of the 21-ketone (152) with oxygen in an alkaline medium afforded the a-hydroxy-acid (153) and the seco-diacid (150). ° Several interesting reactions were observed during this work. ° While pyrolysis of the a-acetoxy-acid (154) yielded the ketone (155) pyrolysis of the seco-diacid anhydride resulted in loss of carbon monoxide and formation of the lactone (156). Lead tetra-acetate oxidation of the ketone (155) [or the hydroxy-acid (153)] followed a Baeyer-Villiger pathway to the lactone (156). The ketone (155) was very susceptible to reduction in the presence of alcoholic alkali. The mass spectral fragmentation of a series of compounds based on 20/8,28-epoxy-18a,19/8H-ursane has been examined. ... 

Corey later described a modification of several steps of his earlier synthesis (see Scheme 1.32). Diacid 171 was smoothly decarboxylated in quantitative yield to give the mono acid 179, which was a-oxygenated as in the previous route. The resulting hydroxy acid 180 was then subjected to oxidative... 

Esterification of acids [1, 192, at end]. In the routine preparation of methyl esters for characterization by gas chromatography by ether extraction and treatment with diazomethane, the extraction step is troublesome in the case of water-soluble acids (e.g., diacids, hydroxy acids). A simple expedient is as follows 143 Assuming that the fatty acid solution is alkaline and free of neutral materials, acidify to pH 3-4 with hydrochloric acid (excess would be converted into methyl chloride), cool (to prevent loss of diazomethane by volatilization), and cautiously (bubbling) add an ethereal solution of diazomethane. 

Mid-chain hydroxy acids are also found. Mosses (Bryopsida, a class of the Bryophyta) contain monohydroxy acids, such as the 7- and 8-hydroxy CJ6 diacids... 

Fatty acid distributions can be affected by microbial oxidation in sediments, so care must be exercised when certain components are used as source indicators. For example, (3-hydroxy fatty acids are produced from (3-oxidation of saturated fatty acids. In addition, C0-oxidation of saturated fatty acids to CO-hydroxy acids and of CO-hydroxy acids to a,CO-diacids is performed by yeasts (unicellular fungi, mainly belonging to the as-comycetes) and bacteria. Consequently, while the long-chain (>C22) CO-hydroxy acids are reliable indicators of higher plant sources, the short-chain components... 

The reaction of trimellitic anhydride (7) with ethanolamine (9) giving the hydroxy acid (10) and with 4,4 -diaminodiphenylmethane (8) giving the diacid (11) has been published in the first poly(ester-imide) patent [l].The second one is nowadays the predominant reaction for making poly(ester-imide)s. Trimellitic anhydride is the basic dianhydride for introducing the imide structure into the polyesters. Nearly every example in patents is based on trimellitic anhydride alone or mixtures with other anhydrides, e.g., tetrahydrophthalic anhydride [59]. The imides made from aromatic anhydrides are thermally more stable than the ones resulting from aliphatic structures (Fig. 4). Both types have been protected by patents, and products made from them are on the market. 

Polyesters. Direct Esterification. Polyesters can be made from hydroxy acids and from diacids and diols by direct condensation ... 

This reaction is best suited for the preparation of low molecular weight polyesters (degree of polymerization, 5-50) of aliphatic hydroxy acids or diacids reacted with glycols having either primary or secondary hydroxyl groups. 

Blends of liquid crystal polymer (LCP) polyester, LCP poly(ester amide) and PAS exhihit a reduced melt viscosity.LCP polyesters are made hy polymerizing aromatic diacids with diols or hy polymerizing aromatic hydroxy acids, e.g. 4-hydroxyhenzoic acid and 6-hydroxy-2-naphthoic acid. In LCP poly(ester amide)s, some of the hydroxyl groups in the monomers are replaced with amino groups. 

A process of polymerization has been described that starts with an acid chloride, and a hydroxy acid in xylene as a solvent. After reaction, the hydrogen chloride is neutralized. In the next step, additional diacid and aromatic diol is added, together with acetic anhydride. Thus the acetylated products are created on the fly in the polymerization vessel. Finally, the actual transesterification polycondensation is performed. ... 

Attempts had been made to synthesise polyesters based on phthalic acid as the diacid component, but these products were amorphous, had low softening points, and were rapidly attacked by organic solvents and acids and bases. Research into polyesters made by the reaction of terephthalic acid (or esters thereof) with aliphatic diols, led to the discovery of polyesters of high commercial value poly(alkylene terephthalate)s [4]. This pairing of diols with terephthalic acid eventually led to the most commercially successful aromatic polyesters, but other synthetic pathways were also investigated towards such products in the early days of polyester development. These included the self-condensation of hydroxy acids of the structure -H0-R-Ph-C02H, where R-OH is para to the acid group and R is -(CH2)- or -(CH2)2- [5], and reactions of aliphatic diacids with 1,4-dihydroxy benzene and similar aromatic diols [6, 7]. Also synthesised about the same time were polyesters based on C2-Cg aliphatic diols and any of the isomeric naphthalene dicarboxylic acids [8]. 

From investigations of non-oxidative degradation, the main products posited from PBT are 1,3-butadiene, THE, 1,4-butanediol and 4-vinylcyclohexane (dimer of butadiene), as well as carbon oxides and water. Potential minor products, as suggested in this theoretical examination, in some way resemble those of PET, with hydroxy acids, hydroxy aldehydes, dialdehydes and diacids. Unlike PET, the above examination reveals the possibility of the formation of unsaturated species such as acids, alcohols and aldehydes which are not possible with PET. One can regard ketene as an unsaturated aldehyde, and acetaldehyde can be derived from an unstable unsaturated alcohol. 

Step-growth polymerization, in which the two types of functional group (A and B) are attached to the same or two different monomers, viz., hydroxy acid (AB) and diol-diacid (AABB). 

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