Chemical Synthesis of Lactic Acids

The commercial process for chemical synthesis of lactic acid is based on lacto-nitrile. Hydrogen cyanide is added to acetaldehyde in the presence of a base to produce lactonitrile. This reaction occurs in the liquid phase at high atmospheric... 

Scheme 1.3 Chemical synthesis of lactic acid via lactonitrile.

Figure 6.7 The chemical synthesis of lactic acid. The d- and L-forms are resolved by distillation after the racemate has been esterified with a suitable alcohol. From Van Ness, J. H. (1978) in Encyclopedia of Chemical Technology, Vol. 13, 85...

Chemical synthesis of lactic acid from lactonitrile is the major alternative process for manufacture in competition with fermentation lactic add. In 1995, synthetic lactic acid accounted for about 50 % of the total world lactic acid production (Litchfield 1996). The advantage of the chemical synthesis route is the ease of obtaining a highly purified lactic acid which is required for many industrial products. The synthetic lactic acid is a racemic mixture (DL), whereas fermentation lactic acid may be selectively D(—) or L(-t) or DL depending on the organism catalyzing the conversion. Controlled optical purity as well as... 

The chemical synthesis of lactic acid consists of the hydrolysis of lactonitrile in the presence of strong acids, and this process yields a racemic mixture of the two isomers (John et al.,... 

Biosynthetic routes often have product-specific advantages over chemical synthesis, which are important for extending and adding value to some bulk products listed in O Table 1.1. For example, optically active compounds, such as lactic acid, can be produced as either l- or o-lactic acid employing specific species of lactobacilli as biocatalysts, whereas chemical synthesis produces a racemic mixture of d, L-lactic acid. Specific properties of polylactide polymers and chemical derivatives of lactic acid differ importantly depending upon the chirality of the monomer (stereospecificity). 

The chemical synthesis of fatty acid esters of lactic acid and lactylates involve protection and deprotection of lactic acid. These methods use strong acid catalysts and high temperatures [73, 74], leading to moderate conversions along with many unwanted... 

Lactic acid, initially produced in 1880, was the first organic acid made industrially by fermentation of a carbohydrate. Nowadays it is made both by fermentation and by chemical synthesis. About 85% of the use of lactic acid is in food and food-related applications, with some use in the making of emulsifying agents and poly(lactic acid). 

Lactic acid is a major end product from fermentation of a carbohydrate by lactic acid bacteria (Tormo and Izco, 2004). However, lactic acid can be produced commercially by either chemical synthesis or fermentation. The chemical synthesis results in a racemic mixture of the two isomers whereas during fermentation an optically pure form of lactic acid is produced. However, this may depend on the microorganisms, fermentation substrates, and fermentation conditions. Lactic acid can be produced from renewable materials by various species of the fungus Rhizopus. This has many advantages as opposed to bacterial production because of amylolytic characteristics, low nutrient requirements, and the fungal biomass, which is a valuable fermentation by-product (Zhan, Jin, and Kelly, 2007). 

As a raw material for the production of monomers used in the synthesis of polymers, to replace oil-derived chemicals, such as polyethylene which can be derived from ethanol obtained by fermentation of starch or of lactic acid, used in the production of polyflactic acid) (PLA) [38]. 

Over the last decade, mounting pressure on crude oil prices together with a desire to move to more sustainable processes pushed many companies to use the fermentation technology even for the synthesis of bulk chemicals. The large-scale productions of lactic acid for polymers and of ethanol as biofuel are two recent examples of this trend. 

Primarily small components are linked to polymers by means of chemical synthesis. These monomers, in turn, are either entirely naturally synthesised - as in the case of lactic acid - or are slightly changed by chemical modification as in the case of different epoxydated sunflower, rapeseed, flax, or soy oils. The latter basic components are still reticulated with hardeners obtained with petrochemicals (some products are, e.g.. Tribest of the 3000 row, PTP, or Elastoflex). But also other natural raw materials such as... 

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. 

The utilization of cellulose as the raw material for production of monomers and polymers is reviewed and discussed. As the most abundant nonfood biomass resource on Earth, cellulose can be catalytically depolymerized to glucose, while glucose is a versatile starting material for a large variety of platform chemicals including ethanol, lactic acid, HMF, levulinic acid, sorbitol, succinic acid, aspartic acid, glutamic acid, itaconic acid, glucaric acid, and so oti. These platforms can be used as monomers directly or further converted to polymerizable monomers for polymer synthesis. 

Some of the fine-chemical manufacturers who supply the pharmaceutical industry now specialize in the use of enzymes for the synthesis of chiral synthons. Chiral cyanohydrins, as well as a- and /S-amino and hydroxy acids, are just a few of the products now available, often produced directly from achiral precursors. Many of the hydroxy acids, such as citric acid (5) and both enantiomers of lactic acid, are fermentation products. The synthesis of some others (Scheme 6.20) resembles the manufacture of aspartate (see... 

Lactic acid used to be an important molecule for the chemical and food industries for centuries. It is produced through anaerobic fermentation by many bacteria. Traditionally its main applications are in the food industry where it is used as a natural acidifying agent. More recently, the scope of its applications was significantly enlarged by the synthesis of polylactic acid (PLA) as a new biodegradable and bio-based bioplastic. ... 

Interestingly, membrane bioreactors produce lactic acid that can be manufactured either by chemical synthesis or by fermentative processes. In recent years, the amount of lactic acid obtained by biotechnological methods has increased. The highest cost in the traditional process of lactic acid production by carbohydrate fermentation lies in the separation steps that are needed to recover and purify the product from the fermentation broth. 

Compared with the chemical synthesis, microbial fermentation for lactic acid production is more ecofriendly, comparatively fast, has superior yields, and can produce one of the two stereoisomers of lactic acid as well as their racemic mixture. It is crucial to select the suitable microbes with high productivity, the low-cost raw materials, and most favorable fermentation conditions, for example, temperature, pH, aeration, agitation, and so on. For development of competitive processes, the search for low-cost raw materials... 

Poly(lactiC acid). Lactic add, CH3CHOHCOOH, occurs naturally in animals and in microorganisms. It can be produced commercially by chemical synthesis, bnt in the United States fermentation is the major route. In bioreactors, microorganisms are fed a carbon source substrate, such as dextrose, with delds of lactic acid greater than 90%. The lactic acid is recovered from the fermentation broth and purified in a multistep process that represents a major part of production costs. Eighty percent of the world s production of lactic acid is from corn sugar. 

The synthesis of lactide was first described by Pelouze in 1845 [71]. He investigated the self-esterification of lactic acid by heating and driving off water and obtained a prepolymer that was no longer fully miscible with water. Upon continued heating of the prepolymer, he noticed that in a certain distillate fraction nice crystals were formed. He was able to deduce the chemical formula and gave the name lactid to the substance. An improved procedure was... 

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