Monophenol yield

Based on our best laboratory data, an economic evaluation of the process showed that it would not be profitable. Earlier studies had shown the opposite. These were based on two optimistic assumptions which were not borne out experimentally (1) that a suitable lignin for hydrogenation could be obtained from spent liquor by a simple autoclaving step, and (2) that the yield of monophenols would be about 40% based on the lignin. Thus, in the economic study, using a more expensive lignin raw material from which lower monophenol yields could be obtained resulted in a poor economic picture. 

To eliminate the high pressure resulting from the excessive water, we studied the use of dried SWL solids in several experiments. It was never possible completely to recover pasting oil when the dried solids were used. At 380°C. the paste oil was nearly recovered, but the monophenol yield was low. At 428°C., the paste oil recovery was lower, and the monophenol yield was higher. In one experiment the dried solids were extracted with liquid ammonia so that carbohydrate material would be removed from the calcium lignin sulfonate. Approximately 10% of the solids were removed... 

A series of runs was made using this work-up. The procedure was satisfactory and gave an average monophenol yield exceeding 20%. An excess of pasting oil was always recovered, and the recycled oil appeared to survive many cycles before it had to be distilled to remove high boilers or pitch. 

Thus, a monophenol yield of about 21% can be obtained with phenol, 0-cresol and m,p-cresol being 13% of the net organic. This yield could be increased somewhat by hydrogenating the excess paste oil which is saved out of each cycle. 

If, by means of catalyst improvements which are not obvious at the present time, the monophenol yield could be improved by, say 50%, the process should become profitable. Another area of improvement lies in reducing lignin preparation costs still further. This is for the future, however. At present, the Noguchi process is the best hydrogenation procedure which has yet been developed for converting lignin into chemicals. 

Noguchi A catalytic process for hydrogenating lignin to a mixture of monophenols. Invented in 1952 at the Noguchi Institute of Japan, but not commercialized because the yields were uneconomic. 

The efficacy of monophenols containing bulky substituents was first described in the patents from Mitsubishi Chemical Corporation [69] (42, Figure 8.17). They report high yields of aldehyde (> 90%) for the hydroformylation of 1-alkenes with high linearities. The l b ratios are generally above twenty using this ligand. 

When the reaction was complete (claimed to be as short a time as one-half hour in some cases), the reaction mixture was removed from the autoclave, and solids were removed by filtering. The liquid product was then distilled. A yield of about 44% of monophenols based on the lignin was obtained with an additional 20-24% of heavy oils, suitable for use as recycling pasting oils. The rest of the lignin was lost as light oil, gas, and water. The monophenol fraction was composed of phenol, 0-cresol, p-cresol, p-ethylphenol and />-propylphenol. 

The monophenol products could not be obtained in as high a yield as originally estimated. 

The apparent yields of monophenol ranged from 15% at 370°C. to 44% at 430°C. Neither the phenol nor the green lignin tar used for pasting oil could be completely recovered, and losses of 20-30% of the pasting oil were noted. Large, pitchy, nondistillable residues were obtained. In addition to the monophenols previously determined by the Noguchi Institute, we confirmed the presence of 0-ethylphenol, 0-w-propyl-phenol, 2,4-xylenol and 2,6-xylenol. 

A paste oil of the estimated composition was made up and used in hydrogenation. The total salable monophenols (b.p., 180°-205°C.) yield from this was found to be 8.5%, and a stabilized lignin tar yield from the second hydrogenator was 19% of the net organic of the lignin. In addition to the yield data, we fractionally distilled the combined monophenol cuts from the continuous runs. The m->p-cresol peak from the gas chromatograph was analyzed by IR spectroscopy and found to be 45% w-cresol and 55% p-cresol, which meant that no pure p-cresol could be obtained by fractional crystallization of the meta, para mixture. From the fractional distillation we found we could obtain most of the monophenols indicated in the gas chromatographic analysis. 

Our many experiments and cost studies showed that either the yield of monophenols had to be markedly increased or the capital and operating costs had to be greatly reduced. We did not see any obvious way to in-... 

Hydroxylation of arenes. Benzene and alkyl derivatives are oxidized to monophenols in 35-60% yield by 30% H202 in combination with HF/BF, etherate at — 78-60°. The reactive reagent is probably H302 + BF4 . 

The norbelladine derivative 408, which served as the starting material for the synthesis of ( )-oxocrinine (415) (Scheme 35), may be readily prepared from the reductive animation of piperonal with tyramine followed by acylation with trifluoroacetic anhydride (191,192). When the N-acylated monophenol 408 was treated with excess thallium tris(trifluoroacetate) in methylene chloride, the di-enone 412 was obtained in 19% yield (191), whereas use of the oxidant vanadium oxyfluoride in trifluoroacetic acid/trifluoroacetic anhydride afforded 412 in 88% yield (192). Base-induced N-deacylation of 412 was accompanied by spontaneous cyclization to furnish racemic oxocrinine (415). Attempts to oxidize the free amine derived from 408 led to the formation of a number of products, some of which resulted from oxidation at nitrogen. 

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