Synthesis of Lactic Acid

In alcoholic solution, lactic ester, for example, methyl lactate can be produced in the presence of a Lewis add catalyst On the contrary, Bronsted acid catalysts such as ion-exchange resins selectively convert GLA/DHA to pyruvaldehyde dimethylacetal via acetahzation of PA. Strong Br0nsted add sites should thus be diminished to avoid this acetahzation Lewis acid sites are responsible for selective formation of methyl lactate [200-202]. However, the rate-determining step for the reaction is considered to be the first dehydration of GLA/DHA to PA, which is accelerated by weak Bronsted acid sites [203]. A bifunctional catalyst with Lewis acid sites and weak Bronsted acid sites, for example, a composite of carbon (weak Bronsted acid) and Sn-sihca (Lewis add) is reported as a fast and selective catalyst for lactic acid and 

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Polylactates are an interesting class of biodegradable polymers which may be made from either renewable or petroleum feedstocks. The synthesis of lactic acid raises real issues concerning the relative greenness of the renewable and non-renewable (HCN) route as discussed in Chapter 2. A summary comparison of the greenness of both routes is shown is Table 6.4. Without a full LCA the choice of route on environmental grounds is not easy and at least partly depends on plant location and raw material availability. 

Strecker, A. The artificial synthesis of lactic acid and a new homologue of glycine. Liebigs Ann. Chem. 1850, 75, 27-45. 

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... 

Lux S, Siebenhofer M (2013) Synthesis of lactic acid frran dihydroxyacetone use of alkaline-earth metal hydroxides. Catal Sd Technol 3(5) 1380-1385... 

Scheme 1.3 Chemical synthesis of lactic acid via lactonitrile.

Scheme 4.22 Synthesis of lactic acid or alanine starting from vinyl chloride via a hydroformylation step.

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...

Scheme 22.5 Synthesis of lactic acid and 5-hydro5 methylfurfural.

Box 2.1 Method for Synthesis of Lactic Acid in Lactate Form—cont d... 

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... 

Unfortunately, literature shows only scarce examples of heterogeneous catalysts performing in the synthesis of lactic acid. The most efficient seems to be the Sn-BEA catalyst, reported by Taarning and coworkers [160] for the isomerization/esterification of triose sugars to ethyl lactate. 

Figure 11.4 Synthesis of lactic acid, lactide and polyjlaclic acid).

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.,... 

Various substrates have been proposed for the synthesis of lactic acid. Many polyols have been reported to be precursors for lactic acid via alkaline hydrothermal conversion. For example, mannitol and xylitol showed a high conversion rate, a maximum LA yield of 25.6% was obtained with sorbitol at 300 °C with 1.75 M NaOH (Zhou et al., 2010). However, studies proved that there is a selectivity of substrates for lactic acid production. This is mainly due to the large number of competitive reactions with the highly functionalized hexitol (Ramirez-Lopez et al., 2010). 

Ramirez-Lopez, C.A., Ochoa-Gomez, J.R., Femandez-Santos, M., et al., 2010. Synthesis of lactic acid by alkaline hydrothermal conversion of glycerol at high glycerol concentration. Industrial Engineering Chemistry Research 49,6270-6278. 

Shen, Y., Zhang, S., Li, H., et al., 2010. Efficient synthesis of lactic acid by aerobic oxidation of glycerol on Au-Pt/Ti02 catalysts. Chemistry-A European Journal 16, 7368-7371. 

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