Terphenyls, hydrogenation

EINECS 262-967-7 Hydrogenated terphenyls Terphenyl, hydrogenated Terphenyl, partially hydrogenated Terphenyls, hydrogenated. 

Bromo-p-terphenyl hydrogenated ca. 0.5 hr. at room temp, and atmospheric pressure with Pd-on-BaS04 and a hydrogen-tritium mixture in ethyl Gellosolve... 

Dowtherm J is a mixture of isomers of an alkylated aromatic that contains only carbon and hydrogen. Dowtherm J can be used in Hquid-phase systems at temperatures as low as —73° C and in vapor-phase systems at temperatures from 185 to 315°C. Dowtherm Q is a mixture of diphenylethane and alkylated aromatics intended for Hquid-phase systems. It can be used at temperatures as low as —34°C. Dowtherm HT is a mixture of hydrogenated terphenyls intended for Hquid-phase systems. Dowtherm HT and Therminol 66 are essentially identical. 

Pyrolysis. Benzene undergoes thermal dehydrocondensation at high temperatures to produce small amounts of biphenyls and terphenyls (see Biphenyl AND terphenyls). Before the 1970s most commercial biphenyl was produced from benzene pyrolysis. In a typical procedure benzene vapors are passed through a reactor, usually at temperatures above 650°C. The decomposition of benzene iato carbon and hydrogen is a competing reaction at temperatures of about 750°C. Biphenyls are also formed when benzene and ethylene are heated to 130—160°C ia the presence of alkaH metals on activated AI2O3 (33). 

As in the case of biphenyl, current worldwide production figures for terphenyls are not readily obtainable, but the volume is probably around 6.8—8.2 million kg/yr. Currently, most of the terphenyl produced is converted to a partially hydrogenated form. U.S. production of terphenyls has remained steady at several thousand metric tons per year over the past decade. The 1991 small lot price for mixed terphenyls was about 3.89/kg whereas the specially fractionated heat-transfer-grade terphenyl—quaterphenyl mixture sold as Therminol 75 heat-transfer fluid was priced around 6.93/kg. Partially hydrogenated mixed terphenyls were priced in the 6.05—7.48/kg range depending on quantity and grade. 

Biphenyl, terphenyl, and their alkyl or hydrogenated derivatives generally serve markets where price and performance, rather than composition, is the customer s primary concern. Performance standards for heat-transfer appHcations are usually set by the fluid suppHer. The biphenyl—diphenyl oxide eutectic (26.5% biphenyl, 73.5% DPO) represents a special case. This composition has become a widely recogni2ed standard vapor-phase heat-transfer medium. It is sold throughout the world under various trademarks. In the United States, Dow (Dowtherm A) and Monsanto (Therminol VP-1) are the primary suppHers. Alkylated biphenyls and partially hydrogenated terphenyls serving the dielectric and carbonless copy paper dye solvent markets likewise are sold primarily on the basis of price and performance characteristics jointly agreed on by producer and user. 

Biphenyl and mixed terphenyls as weU as their normally Hquid alkyl and partially hydrogenated derivatives are commonly stored in the Hquid or molten state. The products are noncorrosive mild steel equipment usually suffices for handling. 

Worldwide production of hydrogenated terphenyls is estimated to be around 9 million kg/ yr with demand remaining faidy steady. Current U.S. prices are in the range of 5.50—6.05/kg. 

Safety. Hydrogenated terphenyls are low in toxicity as the following data (78) indicate. Single exposure (acute) studies show ... 

The formation of o-terphenyl is of special interest, and by isotopic labeling it was shown that this compound is formed by consecutive phenyl and hydrogen migrations. The key intermediate in this sequence of rearrangements is the formation of a highly strained isobenzene (Scheme 20). Several alternative mechanisms are not compatible with the observed distribution of isotopes and could thus be ruled out.106... 

Arylalkenes can undergo various reactions when treated with sodium, since compounds such as a-methylstyrene are both olefins with allylic hydrogens and styrenes, both of which are reactive. The reaction of a-methylstyrene with sodium has been reported by Bergmann et al. (6i) to yield tetramers. More recent work by Kolobielski and Pines (56) has shown that dimers and products derived from dimers are formed when this compound is heated with a sodium-benzyl-sodium catalyst. Some of the major products were cumene (VII), p-terphenyl (VIII), and 1-methyl-1,3-diphenyl-cyclopentane (IX). 

The cyclic diolefin formed can then dehydrogenate as was discussed previously for this type of compound, and the hydrogen eliminated may be transferred to -methylstyrene, as was previously discussed for phenyl-cyclohexene, resulting in the formation of cumene. The diaryldiolefin shown in this mechanism was synthesized and successfully cyclized to p-terphenyl in the presence of sodium 55). 

Physical Form. Liquid the hydrogenated terphenyls are complex mixtures of ortho-, meta-, and p ro-terphenyls in various stages of hydrogenation five such stages exist for each of these three isomers... 

Toxicology. Hydrogenated terphenyls have caused lung, kidney, and liver changes in animals. 

The oral LDso in rats for 40% hydrogenated terphenyls (reactor coolant) was 17.5 g/kg for irradiated reactor coolant it was 6g/kg. Ingestion by mice for 16 weeks of the irradiated mixture at 1200mg/kg was lethal, whereas the nonirradiated mixture was not lethal but did cause irreversible interstitial nephritis. At 250mg/kg, no lesions were observed for tbe 16-week period of exposure. 

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