Document k9E1N0daLzE29dX42M3wKj75n

INTERSCIENCE PUBLISHERS a division of John Wiley & Sons, Neur YorkfLondon !' r. . Copyright @ 1962 by John Wiley C Sons, Inc. . All Rights Reserved Library of Congress Catalog Card Number 58-9220 PRINTED IN THE UNITED STATES OF AMERICA BY MACK PRINTING CO., EASTON, PA. I. General Considerations A. NOMESCLATURE, SOURCES, AND USES O F AROMATIC HTDROCARBOSS The aromatic hydrocarbons contain one or more benzene rings. They are classified into three principal groups, depending on the number of benzene rings and the type of linkage between the rings in the molecule. These groups are: ( 1 ) benzene and its aliphatic and alicyclic derivatives, ( 2 ) polyphenyk-two or more noncondensed rings,and (3)polynuclear-twa or more condensed rdgs. From the industrial hygiene standpoint, the most important aromatic hydrocarbons belong to the first group, consisting of benzene and its aliphatic and alicyclic derivatives. In general, these compounds a x liquids with a significant vapor pressure a t room temperature which, combined with their toxicity, may present potential working hazards. Included in this group are benzene (benzol), toluene, ethylbenzene, styrene, the xylenes, cumene, p-tert-butyltoluene, and tetralin. Benzene and its alkyl derivatives are obtained as by-products of the cokeoven industry and the petroleum industry. From coke-oven operations they are recovered from the gases and the coal tars. As petrochemicals they are separated from crude oil by fractionation, distillation, or solvent extraction, or converted chemically by dehydrogenation of naphthene fractions, alkylation of benzene with olefins, or produced from paraffins by catalytic cyclization and aromatization. Benzene is extensively used as a solvent in the chemical and drug industry, as a starting material and intermediate in the synthesis of numerous chemicals, and as a constituent of motor fuels. Toluene and the xylenes are used as solvents for synthetic rubber, paint and lacquers, and are also constituents of motor fuels. p-Xylene is the intermediate in the synthesis of synthetic fibers. Toluene is the starting material in the manufacture of the explosive trinitrotoluene. Ethylbenzene is used principally as the source of styrene, which is the constituent of polymers such as synthetic p b b e r , plastics, and packaging films. Cumene and p-tertbutyltoluene are used for synthesis in the chemical industry. Cumene is also a Constituent of certain aromatic solvents and motor fuels. Tetralin is prepared by 1219 the hydrogenation of naphthalene and is used as a constituent of solvents, motor fuels, and lubricants. The polyphenyls of industrial importance 3re diphenyl (biphenyl) and the terphenyls (triphenyls) . Diphenyl is produced by thermal dehydrogenation of benzene; terphenyls are by-products in the manufacture of diphenyl. Diphenyl is one of the most thermally stable of known organic compounds. This forms the basis for its use either alone or mixcd with diphenyl oxide as a low-pressure, hightemperature, heat-transfer medium. Dowthcrm A is a eutectic mixture of 73.5 per cent diphenyl ether (diphenyl oxide) and 26.5 per cent diphenyl. The terphenyls are also used as heat-storage and heat-transfer agents. Because of their low vapor pressure and low order of toxicity these hydrocarbons do not present industrial hygiene hazards and do not warrant detailed discussion in this chapter. Naphthalene is the most extensively used polynuclear hydrocarbon in industry. It is the most abundant single constituent of coal tar and is available from this source in technical grades a t a low price. It is important as a starting material and intermediate in the synthesis of numerous chemicals and is used also as a moth repellent and insecticide. B. TOXICOLOGY OF THE AROMATIC HYDROCARBONS The liquid aromatic hydrocarbons are primary irritants which on repeated or prolonged contact with the skin will cause dermatitis due to their dehydrating and defatting action. Contact of the liquid hydrocarbons with lung tissue (aspiration) will cause severe pulmonary edema, pneumonitis, and hemorrhage. Because of their low surface tension a small volume of liquid will cover a large area so that extensive lung injury can result from the aspiration of a few cubic centimeters of a liquid hydrocarbon. The vapors are more irritating to the mucous membranes than equivalent concentrations of the aliphatic and alicyclic hydrocarbons. Systemic injury can result from the inhalation of vapors of the aromatic hydrocarbons. It is well established that benzene (benzol) is an insidious toxicant which has a specific destructive effect on the blood-forming tissue. The preponderance of the evidence from animal experimentation indicates that the alkyl derivatives do not possess this property and that benzene appears to be unique among hydrocarbons as a myelotoxicant. Because the name "alkylbenzenes" suggests to the uninformed that these compounds are similar to benzene, the term "phenylalkanes" has been suggested to dissociate them from ben2ene.l Pharmacologically, the phenylalkanes can be classified with the central nervous system depressants. II. Specific Aromatic Hydrocarbons BENZENE,C a s (Benzol) 1. Sources, U w s , nnd Iiidcrstrinl Exposures t Bcuzeiic (not to 1)c confiiacil wit11 ~ w l r o l ~ ~hiciiniziii, :i 1iytlroc:rrbon uiisturc discuasul iii C!Ilul)tcr 28) is ol)t:iincd ;is :t Iy-l)rocluct of tlic coke-ovcii iiillustry WI. .Gcr;rrdc, A . 1 1 1 A . Arclr. I d . l l e d l l ~1, 9, 403 (195`3). an 93 na Bt. st: as 2. 3. I)(, in i c :I m 4. in hy 30 ho tr: n: VI. rn D D T' br ar L tl IE ir P (1 nts, motor ) and the :nation of Diphenyl forms the iure, highre of 73.5 The ter;e of their 2t present :hapter. in indusable from ;material also as a repeated hydrating 2 (aspira- . Because :a so that meters of embranes 5. aromatic toxicant reponder71 derivale among iggests t o "phenyl- Jogically , sants. I iiiistriro iiiclust r y THE AROMATIC HYDROCARBONS 1221 and the petroleum industry. From coke-oven operations it is recovered from the gases and coal tar. As a petrochemical it is obtained by dehydrogenation of naphthene fractions or by cyclization and aromatization of paraffin hydrocarbons. Benzene is used extensively as a solvent in the chemical and drug industries, as a starting material and intermediate in the synthesis of numerous chemicals, and as a constituent of motor fuels. 2. Physical and Clwrnical Propertirr See Table 1. 3. Determination in the Atinorpfiere I n the presence of other gases the most satisfactory method of determining benzene is the nitration procedure described by Schrenk and co-workers.' The interferoiiieter (Vol. I, page 179), a properly cnlihrnted and serviced benzol indicator, and tlie 1I.S.X. aromatic hytlrocarbon detector may be used for air analysis. 1 mg./liter Z. 313 p.p.in. tinil 1 p.p.ni. Z. 3,19 ing./cu. meter trt 25"C., 7G0 mni. Hg. 4. Physiological Resporrse Acute Toxicity. Acute poisoning by benzene is due to its nnrcotic action and in many respects resembles that caused by other low molecular weight petroleum hydrocarbons. Flury3 gives the following figures for a single exposure for man: 3000 p.p.m.-endurable for 0.5 to 1 hour; 7500 p.p.m.-dangerous after 0.5 t o 1 hour; 20,000 p.p.m.-fatal after 5 to 10 minutes. The inhalation of a high concentration of benzene may cause exhilaration followed by drowsiness, fatigue, vertigo, nausea, and headache. With higher concentrations or longer exposure times, convulsions followed by paralysis and loss of consciousness may result. An initially rapid respiration soon diminishes in rate and circulatory collapse may follow. Death may ensue quickly from respiratory paralysis after severe exposure. Dautrebande' found that dogs inhaling benzene initially developed hypertension. This was soon followed by paralysis of the vasomotor system due to the effect of benzene on the smooth muscle of the blood vessels. High concentrations of benzene are irritating t o the mucous membranes of the eyes, nose, and respiratory tract. Liquid benzene is irritating to the skin and direct contact of liquid benzene with the lung (aspiration) will cause severe pulmonaIy edema and hemorrhage which may be fatal depending on the volume aspirated. Brief exposures to high concentrations in the air may cause chronic benzene intoxication. It is not good practice to encourage or to condone exposure to 100 p.p.m. or more for even brief periods without suitable respiratory protection. A ' H.H.Schrenk, S. J. Pearce, and W. P. Yant, U.S. Bur. Nines Rept. Invest. No. 3287 (1935). a F.Flury, Arch. exptl. Pnthol. Phannakol., 138,65 (1928). ' L. Dautrebande,Arch. intern. phannacodynamie, 44,394 (19%). 101 131 -' 1. 10 0: 3.- 1.. 1.: 17 0.1 1, AI A1 0.' &; - chror It is poisc plete blooi cxpo by 3 mnrr Sign: irrit: TABLE operties of P 16 348 !63 I319 im. !7.3O0C.) i666 ? 17.3"C.) 5 (27C.) .8 duble y soluble y soluble 34.60 F. it be pern. I f benzene istrial use :benzene emia and :s on 102 agnosis of 'ozicol., 21, THE AROMATIC HYDROCARBONS 1223 1 Some Aromatic Hydrocarbons Ethylbenzene 106.16 136.187 -94.950 1.49319 Cumene 120.19 -152.393 96.028 1.48874 Styrene 104.14 145.2 -30.628 1.5441 p-fett Butyltoluene 148.24 192.8 1.4892 10 mm. 10 mm. 4.3 mm. 0.65 mm. (25.90"C.) (38.33"C.) (15C.) (25C.) 0.86258 0.85748 0.9021 0.8575 3.7 4.2 '_ 3.6 1.32 (26C.) 1.03 (26C.) 1.32 (38.3" C.) 1.03 . (38C.) 0.57 (15C.) 1.02 (15C.) 1.00459 (25C.) Naphthalene Tetralii 128.16 217.9 80.22 1.58218 (at 99.6") Approx. 0.082 rnm. (25C.) 1.145 (20"/4"C.) 4.4 132.20 207.2 -30.0 1.54614 (at 20.2") 0.971 (20"/4"C.) 4.6 0.01 (25C.) 1.00 (25C.) 174.6 0.014 g. per 100 ml. (15C.) Miscible 166.2 Insoluble Soluble Miscible Soluble 0.94-6.70 0.88-6.50 265 0.31 g. per 100 ml. (25OC.) Miscible Insoluble Miscible N i i b l e Miscible 1.10-6.10 3 mg.per 100 Insoluble ml. 4.2 g. per 100 Very soluble ml. (20C.) Very soluble Very soluble 0.88-5.9 63F 102OF. 86F. 15SoF.(t.0.c.) 176F. ca. 172F. chronic benzene poisoning varying in seveiity was made in 74 men in this group. It is significant that in this group were found men with clinical pictures of benzene poisoning whose blood was normal, and serious blood abnormalities in the complete absence of signs or symptoms of benzene poisoning. A few men developed blood abnormalities in a 60-day period after removal froiu the source of benzene exposure. The percentages of the positive diagnoses of benzene poisoning detected by any single laboratory blood test in this group are given in Table 2. The bone marrow in chronic benzene poisoning may appear normal, aplastic, or hyperplastic. Signs and symptoms may include headache, dizziness, fatigue, loss of appetite, irritability, nervousness, nosebleed, and other hemorrhagic manifestations. 1224 r3t of Thi or lab SUI 3rc of 1 inn ren eff e of 7 out the ber dai tior con kno mer hoa, deb ?Or urir phe, per: beli ind 5. 1 6. C t positive 4.9 3.5 I .o 0.5 0.5 ,ts almost ex,on of the cir3eing reachetl bsorption and for completc 1 in blood and veen room air if benzene per be stated as e blood is 2.1 iod circulates, j store quanti'ess in reverse picked up by rium with the ver the liquid rise from im' skin contact . even second:re as toluene, istillates. sidized in thc liver with sulea1 sulfates to he severity of my particular benzene in a ncentration in room air.6 TS, J. I n r I . Hilo. nvest. No. 3302 The over-all or integratctl exposure n u y Le best arrived a t by determining the ratio of inorganic to organic sulfates in a sample of urine collected near the end of the day's exposure, or within one hour after cessation of the day's exposure.*V9 The ratio of inorganic sulfates to total sulfates in the urine is normaIly 85 per cent or above. Upon exposure to benzene this ratio is decreased, and the decrease is related quantitatively t o the severity of the exposure to the point where nearly all sulfates are eliminated as organic sulfates. Ratios of less than TO per cent inorganic are 3bn01?nal and may be indicative of benzene exposure and warrant investigation of exposure sources with a view toward correction. Ratios of 60 per cent or less inorganic indicate dangerous exposures xarranting immediate correction. Concurrent exposure to carbon tetrachloride, or any other material having an adverse effect upon the liver, may decrease the sulfate response so that ratios on the order of 70 per cent inorganic would indicate exposures of great significance. As pointed out in the original paper,8 the sulfate test must be made while the worker is on the job, and it is not to be considered a method for diagnosing benzene poisoning, because the changes are merely indicative of exposure, not of poisoning nor of damage. It is therein that the great preventive value of this test lies; the indication occurs in advance of any demonstrable harmful effects, but forewarns of their coming if exposures are not reduced. However, in complete disregard of these wellknown facts, case histories of benzene poisoning too often carry enlightening comments to the effect that from a prognostic viewpoint repeated blood studies on the hospitalized patient are of greater value than concurrent repeated urinary sulfate determinations ! It seems logical to make periodic hematological studies of the blood of all workers coming in contact with any benzene vapors, perhaps every 30 days, and urine sulfate tests, perhaps weekly. Air analyses for benzene in suspected atmospheres should be made frequently. If these three control measures are consistently performed and heeded, as a guide for elimination of significant exposures, it is believed that no fear need be entertained regarding the careful use of benzene in industrial processes. 5 . Hygienic Standard of Permissible Exposure The threshold limit for benzene has been established a t 25 p.p.m. 6. Odor and Warning Properties Benzene has a distinctive odor which should be familiar to all industrial hygienists. The warning properties, however, are inadequate since 100 p.p.m. has an irritation rating of zero and an odor intensity between 1 and 2. W. P.Ysnt, H. H. Schrenk, R. R. Sayers, A. .I. Horvnth, and W. H. Reinhart, J . Ind. Ilyg. Toncol., 18, 69 (1936). JV. P Tmt.H. H. SchrPnk, 2nd F.A. Pnttv,J. Irrd. Flyg. Tom'rol. 18, 319 (1936).