of the light emerging from it. Mixing that light with the light from the uncoated fiber gives an interference fringe pattern that moves as the coated fiber changes its length in response to changes in the hydrogen concentration. An interferometer is used to detect changes in the pattern. Although not yet demonstrated, Butler predicts that such a sensor can be designed to detect as low as 1 ppm hydrogen. The sensor's response time—on the order of minutes—isn't particu-
cerium, and lanthanum were also used. The predominant liquid products were higher alcohols, with isobutyl alcohol being the principal liquid. Labeling studies indicate that the source of the carbon in the higher alcohols was the methanol. Also formed were gaseous products, including carbon monoxide, hydrogen, methane, and lesser amounts of carbon dioxide, ethylene, acetylene, and higher hydrocarbons. The rare-earth acetylides tended to give more gaseous products, which were shown to issue from the methanol. The mechanisms for this chemistry are still under debate. However, lectivity to the 1SO-C4 products. The formation of higher alcohols from Fox has proposed a mechanism that methanol in the presence of the met- explains the results of the research al acetylides is not catalytic. There at Sohio. The formation of the highwould be little commercial interest er alcohols can be explained by in the homologation for that reason, again using the formaldehyde interbut the similarities with the carbon- mediate and using the sequence of carbon bond formation in the iso- aldol condensation and Cannizzaro synthesis process may be quite rele- reactions, followed by hydrogenolysis of the appropriate glycol. D vant to isosynthesis research. Fox notes that calcium carbide has been used to further promote methanol synthesis with the usual zinc oxide/copper catalysts to increase the yield of isobutyl alcohol. At high temperatures, methanol can be converted to isobutyl alcohol alone with calcium carbide. Fox and his associates have tested this idea in a fluidbed reactor operating from 300 to SWITCH TO 450 °C. In addition to calcium ENGELHARD carbide, the carbides of sodium, CATALYSTS FOR: larly fast, Butler says, because it is governed by the surface chemistry of molecular hydrogen interacting with the palladium coating, rather than simply diffusion of the hydrogen into the coating. Molecular hydrogen must attach to the palladium surface, be split to atomic hydrogen, and diffuse into the palladium. Calculations suggest that the use of other coatings, particularly certain polymers, can extend the concept to sensors for other chemicals, Butler says. D
New insights gained on C-C bond formation The degree of current interest in Fischer-Tropsch chemistry (and its close relative, the isosynthesis process) reflects its commercial potential. It also suggests that there is much to investigate before basic Fischer-Tropsch chemistry is understood. Sometimes the key to understanding one area of chemistry originates in a neighboring field of research. A case in point was described at the recent American Chemical Society meeting in Philadelphia by Joseph R. Fox, a research chemist at Standard Oil Co.'s (Ohio) research center in Warrensville, Ohio. He is concerned with the formation of carboncarbon bonds in methanol in the presence of metal acetylides. Like the isosynthesis catalysts, the acetylides appear to provide unusual se-
Are you still brewing your own?
Mechanism for forming higher alcohols from methanol -H, CH3OH2CH 2 0 •
CH 2 0 Base
OHC-CH 2 OH + 2CH 2 0
-•OHC~CH2OH
Base
ChLOH I 2 - • HO-C-CHO I CH2OH CH0OH
CH2OH H O - O - C H O + CH 2 0·
Cannizzaro
-•HO-C-CH2OH
CH2OH CH2OH I H O ~ C - C H 22O H + 3H 2 I CH2OH
CH2OH ChL
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- • HC-CH 2 OH + 3H 2 0
ÊEN€=ELM£Mnt»
September 24, 1984 C&EN
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