A life cycle thinking analysis (LCT) conducted on the production of vanillin via bamboo wet air oxidation compared to vanillin production from crude oil or kraft lignin.

Hydrogenolysis of cork has been examined using a range of precious metal catalysts studying the effect of the support, added base and solvent used.

Hydrogenolysis of bark from three different species of tree using heterogeneous platinum group metal catalysts produces two major product streams. Aromatic substituted guaiacols are produced from lignin and the lignin-like regions of suberin and a range of saturated fatty acids and alcohols, including alpha,omega-functionalised species, are produced from the polyester regions of suberin. Control experiments demonstrate clear advantages of catalytic hydrogenolysis over base hydrolysis, both in terms of conversion and product selectivity.

The commercial production of vanillin from sodium lignosulfonate under highly alkaline conditions, catalyzed by Cu2+ at elevated temperature and pressures up to similar to 10 bar, has been simulated in a 3-L stirred reactor. Initially, the process was operated in the presence of nitrogen in dead-end mode, and it was shown that vanillin and vanillic acid were formed by hydrolysis at temperatures of 120, 140, and 160 degrees C. At the two higher temperatures, the amount of vanillin produced was the same. Subsequently, experiments were conducted at the same elevated pressures and temperatures with addition of air or oxygen enriched air once the temperature in the reactor had reached temperatures similar to those used when only hydrolysis occurred. In this case, the concentration of vanillin at 140 and 160 degrees C was equal to that due to hydrolysis, and the subsequent 2-fold increase was due to oxidation. In addition, both vanillic acid and acetovanillone (which has rarely been reported) were produced, as was hydrogen. Thus, for the first time, it has been shown that the production of vanillin (and other compounds) from sodium lignosulfonate at elevated temperatures involves hydrolysis and oxidation, with hydrolysis starting at just above 100 degrees C, that is, much lower than has previously been reported. Approximately 50% is produced by each mechanism. In addition, the orders of the reactions of the different steps were estimated, and the reaction mechanisms are discussed.

The use of model compounds in the development of selective lignin depolymerisation processes has been limited by the lack of complexity of these models compared with lignin itself. In this paper we report a convergent and efficient synthetic method for the flexible, multi-gram preparation of model lignin hexamers and octamers containing three of the most common connectivity motifs found within native lignin, namely β-O-4′, 5-5′ and β-5′, which will be used to further the mechanistic understanding of lignin depolymerisation processes.

The production of vanillin from sodium lignosulfonate under highly alkaline conditions, catalyzed by Cu2+ and at elevated temperature and pressures, has been studied in two sizes of stirred reactors. The larger reactor (3 L) was operated in both the dead end and the gas throughflow modes; the sparged gas was nitrogen and "simulated air" in the former case and air in the latter. The smaller reactor (300 mL) was only operated in the batch mode with oxygen. In the 3 L reactor, with nitrogen gas alone in the dead end mode, vanillin was produced by hydrolysis. With the other conditions, both hydrolysis and oxidation occurred and the amount of vanillin produced was greater. In addition, for the first time since this process was first introduced in 1936, the composition of the gas phase produced by the reaction was investigated, too. The measurements were made on samples taken from the headspace of the 300 mL batch reactor and the headspace of the 3 L reactor in the dead end mode and in the exhaust gases in the throughflow mode. It was found that, whenever vanillin was produced, hydrogen was detected in the gas phase. In the 3 L reactor in the dead end mode, the amount of H-2 formed was so great (similar to 7% by volume) in the case of "simulated air" that the production of vanillin ceased as no further air (oxygen) was able to enter the reactor. In the throughflow mode, the concentration of hydrogen detected in the exit gas was much lower as it was flushed out in the exhaust. As a result of the different levels of oxygen and hydrogen in the reactor in the dead end and throughflow modes, the amount of vanillin produced was greater in the latter case. Thus, it is difficult to use studies in the dead end mode to predict the behavior in throughflow, the mode generally used industrially.

A series of 2-, 3- and 4-substituted pyridines was metabolised using the mutant soil bacterium Pseudomonas putida UV4 which contains a toluene dioxygenase (TDO) enzyme. The regioselectivity of the biotransformation in each case was determined by the position of the substituent. 4-Alkylpyridines were hydroxylated exclusively on the ring to give the corresponding 4-substituted 3-hydroxypyridines, while 3-alkylpyridines were hydroxylated stereoselectively on C-1 of the alkyl group with no evidence of ring hydroxylation. 2-Alkylpyridines gave both ring and side-chain hydroxylation products. Choro- and bromo-substituted pyridines, and pyridine itself, while being poor substrates for P. putida UV4, were converted to some extent to the corresponding 3-hydroxypyridines. These unoptimised biotransformations are rare examples of the direct enzyme-catalysed oxidation of pyridine rings and provide a novel synthetic method for the preparation of substituted pyridinols. Evidence for the involvement of the same TDO enzyme in both ring and side-chain hydroxylation pathways was obtained using a recombinant strain of Escherichia coli (pKST11) containing a cloned gene for TDO. The observed stereoselectivity of the side-chain hydroxylation process in P. putida UV4 was complicated by the action of an alcohol dehydrogenase enzyme in the organism which slowly leads to epimerisation of the initial (R)-alcohol bioproducts by dehydrogenation to the corresponding ketones followed by stereoselective reduction to the (S)-alcohols.

Biotransformations of a series of ortho-, meta- and para-substituted ethylbenzene and propylbenzene substrates have been carried out, using Pseudomonas putida UV4, a source of toluene dioxygenase (TDO). The ortho- and para-substituted alkylbenzene substrates yielded, exclusively, the corresponding enantiopure cis-dihydrodiols of the same absolute configuration. However, the meta isomers, generally, gave benzylic alcohol bioproducts, in addition to the cis-dihydrodiols ( the meta effect). The benzylic alcohols were of identical ( R) absolute configuration but enantiomeric excess values were variable. The similar (2R) absolute configurations of the cis-dihydrodiols are consistent with both the ethyl and propyl groups having dominant stereodirecting effects over the other substituents. The model used earlier, to predict the regio- and stereo-chemistry of cis-dihydrodiol bioproducts derived from substituted benzene substrates has been refined, to take account of non-symmetric subsituents like ethyl or propyl groups. The formation of benzylic hydroxylation products, from meta- substituted benzene substrates, without further cis-dihydroxylation to yield triols provides a further example of the meta effect during toluene dioxygenase-catalysed oxidations.

A previously unreported alcohol dehydrogenase enzyme in the mutant soil bacterium Pseudomonas putida UV4 catalyses the reduction of 2-, 3- and 4-acylpyridines to afford the corresponding (S)-1-pyridyl alkanols, with moderate to high e.e., whilst under the same conditions 2,6-diacetylpyridine is readily converted to the corresponding enantiopure C2-symmetric (S,S)-diol in one step. In contrast, the toluene dioxygenase enzyme in the same organism catalyses the hydroxylation of 2- and 3-alkylpyridines to (R)-1-(2-pyridyl) and (R)-1-(3-pyridyl)alkanols. This combination of oxidative and reductive biotransformations thus provides a method for preparing both enantiomers of chiral 1-pyridyl alkanols using one biocatalyst.