Glycolic acid Chemical synthesis

Other possible chemical synthesis routes for lactic acid include base-cataly2ed degradation of sugars oxidation of propylene glycol reaction of acetaldehyde, carbon monoxide, and water at elevated temperatures and pressures hydrolysis of chloropropionic acid (prepared by chlorination of propionic acid) nitric acid oxidation of propylene etc. None of these routes has led to a technically and economically viable process (6). 

The transformation of raw materials into products of greater value by means chemical reaction is a major industry, and a vast number of commercial prod is obtained by chemical synthesis. Sulfuric acid, ammonia, ethylene, propyl phosphoric acid, chlorine, nitric acid, urea, benzene, methanol, ethanol, ethylene glycol are examples of chemicals produced in the United States, billions of kilograms each year. These in turn are used in the large-scale manu ture of fibers, paints, detergents, plastics, rubber, fertilizers, insecticides, Clearly, the chemical engineer must be familiar with chemical-reactor design operation. 

Use Source of glycolic acid and of the glycolic acid radical in chemical synthesis. 

About 75% of the n-butyraldehyde generated is converted into 2-ethylhexanol, which is almost completely consumed as a phthalate ester, e.g., in plasticizers for PVC. The remainder of the butyraldehydes are either used as such for chemical synthesis, converted to acids or amines, or - more important today - hydrogenated to the butanols which are either directly sold as solvents or are further converted into acrylate esters, glycol ethers, butyl acetate, and butyl amines. 

Polymers derived from renewable resources (biopolymers) are broadly classified according to the method of production (1) Polymers directly extracted/ removed from natural materials (mainly plants) (e.g. polysaccharides such as starch and cellulose and proteins such as casein and wheat gluten), (2) polymers produced by "classical" chemical synthesis from renewable bio-derived monomers [e.g. poly(lactic acid), poly(glycolic acid) and their biopolyesters polymerized from lactic/glycolic acid monomers, which are produced by fermentation of carbohydrate feedstock] and (3) polymers produced by microorganisms or genetically transformed bacteria [e.g. the polyhydroxyalkanoates, mainly poly(hydroxybutyrates) and copolymers of hydroxybutyrate (HB) and hydroxyvalerate (HV)] [4]. 

Lactic- and glycolic acids can be manufactured by (a) chemical synthesis or (b) carbohydrate fermentation. 

The next two sections of this review chapter will introduce the reader to the world of lactic acid. The acid is both a key platform chemical of the biorefinery concept, from which other interesting molecules may be formed (Sect. 2), and a monomer for commercial bioplastic polylactic acid (PLA) (Sect. 3). In the platform approach, the assessment from Chap. 1 in this volume [23] proves its value, as it is an equally useful tool to seek out the most desired routes for transforming a biomass-derived platform molecule as it is to select the most relevant carbohydrate-based chemicals from a chemist s point of view. In what follows, the desired catalytic cascade from cellulose to lactic acid will be described (Sect. 4) as well as the specific catalytic data reported for different feedstock (Sects. 5 and 6). Section 7 will introduce the reader to recent synthesis routes for other useful AHA compounds such as furyl and vinyl glycolic acid, as well as others shown in Fig. 1. Before concluding this chapter, Sect. 8 will provide a note on the stereochemistry of the chemically produced AHAs. 

Lactic acid can be produced from chemical or biotechnological methods. Chemical synthesis is based on the hydrolysis of lactonitrile by strong acids, or by base catalyzed degradation of sugars, oxidation of propylene glycol, or by chemical reactions of acetaldehyde, carbon... 

Two molecules of lactic acid can be dehydrated to lactide, a cyclic lactone. Then, polymerized to lactide to either heterotactic or syndiotac-tic polylactide, which is also called PLA. Lactic acid can be produced from chemical or biotechnological methods. Chemical synthesis can be based on the hydrolysis of lactonitrile by strong acids, or by base-catalyzed degradation of sugars, oxidation of propylene glycol, or by chemical reactions of acetaldehyde, carbon monoxide, and water at elevated temperatures (Mussatto et al. 2008). 

It is a prerequisite that after implantation of the newly established tissue into an organism the scaffold, as a foreign material, should show clear effects of bioerosion and bioresorption under the influence of cells after a short period. A few polymers exhibit this behaviour, such as polyesters like poly(lactic acid) (PLA), poly(glycolic acid) or their copolymers poly(lactic-co-glycolic acid) (PLGA). Polyphosphazenes are known to be converted into harmless phosphates and ammonia salts and, together with residues of carbon-based side arms, should be excreted easily from the body. Furthermore, polyphosphazenes and their properties can be tailored, leading to defined bioresorption kinetics, defined pore sizes and defined additional chemical functionalities. Thus, polyphosphazenes can be considered as extraordinary materials for the synthesis of scaffolds to be applied in TE. 

In the chemo-enzymatic synthesis of LLG-3 performed by Withers et al. [34], the glycoside of 8-0-Me-Neu5Ac with glycolic acid 59 was synthesized from NeuSAc derivative 58 by a chemical method because of the absence of a sialyltransferase capable of sialyltransfer to the hydroxyl group of the glycosyl amide in the penultimate sialic acid residue and an 8-O-methyltransferase for NeuAc (Scheme 11.10). 

Petricca SE, Marra KG, Kumta PN (2006) Chemical synthesis of poly(lactic-co-glycolic acid)/hydroxyapatite composites for orthopaedic applications. Acta Biomater 2 277-286... 

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