Properties and Uses of Pentachlorophenol T. S. CARSWELL AAD H. K. NASON Monsanto Chemical Company, St. Louis, Mo.
iiiore acidic than phenol itself. I t rea,cts quantitatively with caustic alkalies to give alkali salts whicli can be recovered in solid form by evaporation. The sodium salt is quite soluble in water, where= t.he free phenol is not; hence, the dry sodium salt is marketed for those applications where a water-soluble form is desired. Pentachlorophenol, dissolved in dilute alcohol, can be quantitatively titrated with standard caustic alkali solutions. Thymol blue can be used ns an indicator, or the end point, may he observed elcctrometrically, as a sharp change in potential takes place at the end point. The pII value of a 1 per cent solution of sodium pentnchlorophenatc is approximately 8.0; the pH values of 5 and 25 per cent solutions are about. 9.6 and 10.5, respectively. I'entachlorophenol is quite stable snd does not undergo decomposition even when heated for extended periods a t elevated temperatures. It does not split off chlorine to a measurable extent when boiled with water or aqueous acid solutions; the chlorine is apparently bound firmly t,o the benzene ring. Since i t is a phenolic body, pentachlorophenol undergoes, in a genernl way, the usual reactions of phenols. Ifowever, the presence of five chlorine atoms rnakes the hydroxyl group less reactive in many instances. Since all of the ring hydrogen atoms heve been replaced by chlorine atoms, coupling or substitution reactions commou to most phenols do not occur. With the heavy metals, conipormds are iormed which we water insoluble and which are in some cases highly colored. Copper pcntachlorophenate, for example, is purple. the silver
Pentachlorophenol, which was first described in 1841, is now being produced commercially in the United States. The physical and chemical properties are reported in detail, and the toxicological characteristics are briefly outlined. These properties render pentachlorophenol particularly attractive as an agent for the control of micro6rganisms, and its application in this field is described. Its uses include the preservation of wood and wood products, pulp and paper, textiles, starches and dextrins, gums, glues, casein, albumin, leather, and latex. It is also valuable for slime and algae control.
ENTACHLOKOPHESOL was first prepared in 1841 by Erdmann (8),who obtained it by the action of chlorine on an alcoholic solution of chloroisatin, dichloroisatin, or indigo. He did not, however, correctly determine the structure of his product, which he named gechlmte chlorindopten and to which he assigned the formula C,GchoH,, thus failing to recognize ita phenolic nature. Laurent (6) in 1843 repeated the analysis and proposed the HpO. The preparation by chlorination formula C,,CI,eO of phenol was reported by Laurent (7) and by Schutzenberger (11). In 1872 Mere and Weith (8) prepared pentachlorophenol by the practical method of directly chlorinating phenol in the presence of a catalyst, and this method was improved in 1883 hy Bendikt and Schmidt (9). Although the existence of pentachlorophenol as a chemical compound has long been recorded in the literature, it was never produced on a commercial scale until 1936, nor were ita properties and potential uses appreciated before the oommercial development. Since then a number of uses have been found for the material; most of them are due to its unusually high degree of effectiveness in biological control, combined with its desirable physical properties. Chemically, pentachlorophenol is simply phenol which has been chlorinated as completely as possible without destruction of the benzene ring; all of the ring hydrogen atoms of phenol are thus replaced by chlorine. The pure compound contains 27.03 per cent carbon, 66.59 chlorine, 6.00 oxygen, and 0.38 hydrogen. Its molecular weight is 266.4. Pentachlorophenol is a fairly weak acid, although the presence of the chlorine atoms, as would he expected, makes i t
+
DIFFERENCE XN FUNWJS GEOWTH ON ANMAL GLUE WITR AND WITHOCT THE ADDITION OF 0.25 PERCENTSODIUM PENTACHLOROPHENlTE
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JUNE, 1938
623
handling of the material and to eliminate unforeseen toxic reactions among industrial workers. The toxicity of pentachlorophenol to rabbits and guinea Physical Properties pigs was determined by Kehoe ( 5 ) . The chemical is a general organic poison and, if administered in sufficient and forms PentachloroPhenol is a white quantity, can cause death upon ingestion, absorption through crystals with a crystallizing point of 190.2" C. the skin, intravenous injection, or subcutaneous injection. The solubility in water is very slight and is shown in the The minimal lethal dose L. D.) varies with the type of following table: animal, method of administration, and solvent employed. Temp. Solubility Temp. Solubility The M. L. D. for rabbits intravenously injected with a water solution of the sodium salt is about 36 mg. per kg. of C. Gram/100 grama soln. C. Gram/100 grama s o h . 0 0.0005 62 0.0058 body weight. The corresponding value for subcutaneous 50 27 0.0035 0.0018 70 0.0085 injection is about 60 mg. per kg. and for cutaneous application about 260 mg. per kg. Guinea pigs give about the same results. The M. L. D. of the free phenol applied cutaneThese data are shown graphically in Figure 1. ously to rabbits varies widely with the solvent; it is 39 mg. T h e solubility in common organic solvents is given in per kg. in pine oil, 100 in petroleum distillate, and considerTable I. It should be noted that pentachlorophenol tends to form supersaturated solutions in many organic solvents. ably over 300 in ethanol. Bechhold and Ehrlich (1) found the M. L. D. to white mice, T h e data given in Table I were obtained by adding pure pentachlorophenol to cold solvent and raising the temperaintravenously injected with a water solution of the sodium ture slowly with agitation until solution took place. salt, to be 56 mg. per kg. When lethal doses are administered, the symptoms are those of pronounced toxemia. Fever, increased respiration and heartbeat, hyperTABLE1. SOLUBILITY OF PENTACHLOROPHENOL IN ORQANICSOLVENTS glycemia, and glycosuria are induced and progress Solubility Qrams/100 Grama S o h . rapidly. A complete loss of muscle tone beSolvent h0 C. loo C. 20'6. 30° C . 40OC. 50° C. 6OOC.' comes apparent from 30 to 10 minutes before 72.0 Methanol 40.5 48.0 57.0 65.5 75.5 77.5 49.5 53.0 56.5 63.5 60.0 67.0 Anhydrous ethanol 46.0 death, and the animals die in B state of com65.0 39.5 48.0 57.0 64.0 Butyl Carbitol 34.5 62.0 43.0 47.5 52.0 61.0 95% ethanol 39.0 56.5 65.5 plete collapse, with pronounced evidence of cir39.0 28.0 32.0 35.5 43.0 Pins oil 24.5 46.5 culatory failure. 30.0 40.0 62.0 51.0 Carbitol .. *. .. 52.5 64.5 62.0 27.5 Diethylene glycol .. No animals died later than 6.5 hours after appli50.0 27.0 37.5 65.0 Cellosolve 8 :0 li :o 22.0 11.5 16.0 30.0 Dioxane .. 5.5 37:5 cation of the chemical; i. e., the animals which sur11.0 14.0 19.5 24.5 Benzene 31.5 vived the most severe acute symptoms and lived 11.5 15.5 20.5 Technical o-dichlorobenzene 5 :5 6:5 8.5 26.0 11.6 21.0 6.0 31.5 38.5 Ethylene glycol 6.5 hours did not suffer from severe delayed for 2:4 4.0 Diesel.oila i:9 3.1 5.7 8.2 11.3 5.4 7.8 3.7 1.8 2.6 Fuel oilb .. toxic effects or from secondary complications. 3.5 5.5 0.5 1.5 2.5 Stoddard AolventC .. ?:5 Apparently there is no cumulative action since 5 Obtained from Magnolia Petroleum Compan no damage was found to result from the repeated b Known aa N o 2 fuel oil obtained from Shell &roleurn Cor oration. c A grade of pe'troleum sklvent dascribed in Bureau of Stan&& Booklet CS3-28. administration of sublethal doses of the chemical I on successive days. compound is golden yellow, and the mercury salt is lemon yellow.
0
7
1
Pentachlorophenol is practically insoluble in aqueous ammonia solutions. The vapor pressure of pentachlorophenol was determined by the static method a t temperatures between 100" and 220° C., and these values are plotted in Figure 2 , using the customary relationship for such data: log P = ( l / T )
+K
From this curve, vapor pressures a t various temperatures were read, and these data are shown in the following table: Temp. C.0 20 50 75
Vapor Pressure Mm. Hg
0.000017 0.00017 0.0031 0.024
Vapor Vapor PresPresTemp. sure Temp. sure C. M m . H g O C . M m . H g 180 10.9 100 0.14 200 25.6 120 0.49 220 56.2 140 1.5 240 116.3 160 4.3
,
$
.0.0090
'4
0.0010
$
I
0.0060
/
0.ow0 0.0050
oa#o
0.
f
0.#30
g
0.0020
Vapor
Temp.
' C.
260 280 300 300.06
Pres-
sure M m . Hg 227.7 424.7 753.4 760.0
The very low vapor pressure of pentachloroqhenol a t ordinary temperatures is of great advantage in uses where lack of volatility is essential.
Toxicity It is as important to know the toxicity of a new compound before it is placed on the market as it is to know its chemical and physical properties. This knowledge enables one to fake such precautions as are necessary to ensure the safe
/0
20
39
443
i ' k - w r wee ~~
50
60
;7
OC.
FIGURE 1. SOLUBILITY OF PENTACHLOROPHENOL IN WATER
An oil solution of pentachlorophenol or a water solution of its sodium salt causes irritation and dermatitis in the case of small laboratory animals if allowed to remain on the skin a sufficient length of time. This dermatitis clears up rapidly after exposure to the chemical is discontinued, and the lesions heal without scars or other residual effects. These observations indicate the general effects of the absorption of pentachlorophenol and show that, although it is less toxic than many chemicals in everyday use, a certain degree of potential hazard does exist in connection with its use. Experience has shown that the health hazard may be
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INDUSTRIAL AXD ENGINEERIKG CHEMISTRY
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rendered entirely negligible by intelligent handling and by the use of protective garments.
Uses The most important use for pentachlorophenol is in the field of industrial preservation, where its high degree of toxicity to fungi, bacteria, yeasts, algae, protozoa, and other microikganisms, combined with its unusual physical and chemical properties, renders it particularly effective. The fungicidal values of pentachlorophenol and its sodium salt, as determined by the standard Petri plate test (IO), are given in Table 11. For comparison, the corresponding data for @-naphthol and p-chloro-m-eresol, two chemicals i r e quently used as fungicides, were determined by the same method and are shown in the table. Pentachlorophenol is a very effective fungicide against. widely different types of organisms. Also, sodium pentachlorophenate is as t.oxic as the free phenol. Many phenolic
fungicides are markedly less active when neutralized with alkali. High degree of toxicity to microorganisms, low water solubility and low vapor pressnre (ensuring permanence), good chemical stability, and availability a t low price combine to render pentachlorophenol particularly valuable as a preservative and especially for the uses described below. WOODPRESERVATION. The largest single use for pentachlorophenol is in the preservation of wood and wood products. There are several methods of application in use; the selection of the proper one depends upon a number of factors, including the type of wood and the purpose for which it is to be used. For long-time preservation, pressure impregnation is the best method that can he relied upon to give a thorough and uniform treatment. For this purpose the use of a 5 per cent solution of peotachlorophenol in a petroleum solvent,such as a fuel oil distillate, is recommended. The wood should be comDletelv saturated with this solution in a Dressnre:treat& cylinder,followingone of the staidard procedures for this type of treatment. Wood so treated is resistant to decay and insect attack and should endure for years under service conditions. It may he used for piling, railway crossties, foundation timber, and for other purposes where permanence under adverse conditions is required and where creosote-treated mood is now used. In addition, wood treated with pentachlorophenol can be used for many purposes for which the undesirable properties of creosote-treated stock render i t inapplicable. For example, wood treated with pentachlorophenol retains its natural appearance, is clean and not discolored, possesses little or no odor, and may be painted as readily as untreated wood. It is easily handled and does not exude materials which stain clothing or other materials with which i t might happen to come in contact. Hence, wood treated with pentachlorophenol will be used in houses and other buildings, loading platforms, shipx, railway cars, fence posts, yardrails, and for many other purposes where permanence, in addition to the natural properties of wood, is desired. The preservat.ion of finished millwork, such as window sash and frames, by a dipping process was described by Hubert
DECAY AND WOOD
‘rERMITX: RDSISTANCE OF WITH PENTACHLOROPIiENOL
BRUSH-TREATED
JUNE, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
(4). In this process the assembled members, or component parts, are immersed in a solution of pentachlorophenol in petroleum solvents. The solution should contain approximately 5 per cent pentachlorophenol; a number of different types of petroleum solvents may be used. The immersion time should be sufficient to obtain good penetration into the wood and varies with the type of solvent, its temperature, and the texture of the wood. In most cases a 3-5 minute dip is satisfactory. I n general, the dipping treatment confers more protection to the cut ends of the wood, since mos6 of the penetration occurs along the grain. However, since these cut ends are the parts most subject to moisture penetration and decay, they require the most treatment. Exhaustive tests by Hubert and others have demonstrated that the dipping treatment, when properly conducted, gives adequate protection for this class of products. In most cases the application of preservative solutions to wood by brushing does not give good protection, since absorption is generally poor across the grain. It has been discovered.,~~ however. that solutions of uentachlorouhenol in certain mid-continent fuel oil dist2lateseve good pinetration even across the grain, and can be applied by brnshingwith tests "wre shows the results Of lahoratov good to determine the fungus resistance of wood treated in this manner. f l d fof the area of a 2 X 4 inch section of southern yellow pine was treated by being brushed with a 5 per cent solution of pentachlorophenol in suitable solvents; the other half of the area was left untreated. After drying, a cross section 0.25 inch thick was cut from the timber and placed in a Kolle Bask containing a mat of the wood-rotting fungus Lenzites Irabea. A similar section cut from an untreated timber was placed in a duplicate flask to serve as a control. The flasks were then incubated 5 months a t 26" C. The portion of the wood which had been treated wa,,not attacked by tho fungus and therefore retained its original strength and properties. The untreated portion and the control section were attacked and completely decayed. The protection on the treated section extended to the center of the block and thus demonstrated the excellent degree of penetration ohtained. Termite resistance was tested by brush treating half tho area of southern yellow pine boards, 1 X 6 x 18 ~
~
625
~
3, Fnxcns of TEEATE. WITa PPE CENTPENTACHL~EOPHEN~L SOI.UTXON (Left) Untreated.
(RivU) Upwr poition, brush-treated: lower Doition. untreated.
inches; these boards are buried in termite-infested soil in Florida. The tests are still in progress, but after 9 months inspection showed that the untreated wood had been attacked by the termites and badly damaged; the treated portion had not been touched. This development of an effective preservative solution nrhich can be applied by painting with a brush is important in that it, makes possible the protection of wood and timbers in existing buildings which cannot be treated by any other method. When logs are sawed into lumber SAPSTAIN CONTROL. and piled in the open to dry, certain fungi grow on and in the sapwood and produce dark-colored nnsightly stains. These sap stains reduce the value of the lumber and lower its selling price. Ti the freshly cut boards are properly dipped in a dilute ayueous solution of sodiom pentac,lilorophenate before being piled in the yards to dry, the fungus growth is preTnxLE 11. l'oxIClTY O F SIIRSTITUTED PHl3XOLS TO PUNCI vented, and the lumber remains clean and _.._____ Perrentare of Cliernical in the Medium----"bright" and brings a full price when --Cawing Total Inhibition-Causing Deathsold. Sodium Sodium I'entsuenta8- p-Chloro- Pentb pCliIoroS1,SME AND ALGAECONTROS,. Modern chioru- ohloro- Nauhm chlo?o- %% N&hmuhenol oheoste tho1 src%o1 nhanol yhenste tho1 eread heat. emineerine nractice ulaces meat emph&is"on cle&' condenser and ither heattransfer surfaces. These surfaces 0.05 0 08 0.00G 0.008 0.01 0.02 0.03 0.06 are frequently fouled by organic dime 0.09 0.04 0.01 0.01 0.1 0.04 0.008 0.008 0.05 0.008 0.2 0.03 0.02 0.01 0.3 0.00s deposits which result from the growth 0.01 0.002 0 02 0.002 0.002 0.02 0.002 0.01 of algae, bacteria, and other miuroib U.li06 0.02 0.02 0.006 0.006 0.02 0.e2 0.006 0.02 0.006 0.02 0.002 0.003 0.02 0.006 0.02 gaiiisms in the circulating water; a great 0.002 0.002 0 02 0.02 0.004 0.004 0.04 0.04 0.002 0.01 0.002 0.002 0.008 0.w2 o,ni 0.008 deal of effort has been directed toward 0.002 0.nul il.002 0.02 0.02 0.a02 0.03 0.02 finding ways to prevent the growth of 0 002 0.002 0.01 0.m 0.004 0.006 0.05 0.04 0 002 0.002 0.02 0.02 0.004 0.0M 0 . 0 3 0.03 snch organisms and thus eliminate the IJ .OOlL o.onib o.on5b 0.004 0 . 0 0 1 b o.onrir n.nobb 0.004 0.02 0.04 0.002 Ii.CO2 0.02 0.002 0.002 0.0s formation of slimes. The best metliods 0.004 0.004 0.01 0.006 0.004 0.008 0.02 0.01 yet developed utilize chemicals which are toxic to the microijrganisrns, and the 0.004 u 004 0.02 0.02 o 004 0 . ~ 0 6 0.02 u 0% addition of chlorine to cooling waters has 0 006 0.008 0.02 0.01 0.03 0U4 been especially successful (9). 0.006 o.oufi 0.01 o:b& 0 ' 0 0 ~ 0.02 0 01 0.008 0.004 0.004 0.01 0.008 0.004 0.0C6 0.02 1>.01 Sodium pentachlorophenate is an effec0.006 0.10 0.02 0.006 0 . ~ 0 6 0.006 0.25 0.04 0.004 0.008 0 ~ 0 2 0.01 0.008 0.008 0.08 0 01 tive toxic chemical for the prevention 0.01 0.01 0.02 0.02 0.02 11~02 0 . 0 3 CJ 03 of slime and algae deposits. It appears Formerly known w . Fomea onnorus. to he toxic to many types of organisms b Or less. which are resistant to chlorine and has e Obtained from R. E. Waterman. Bell Telephone Laboratories. been used successfully in several casea
__
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INDUSTRIAL AND ENGINEERING CHEMISTRY
where other toxics had previously failed. Its chief appliestinn is in industrial coolinb. svstems. narticulsrlv in those plants which are too small to iustify t i e installaiion of the eanimnent needed for the use of chlorine. The chemical is e&&d to find application in industrial cooling-water systerns hut will probably never replace chlorine for domestic water supplies.
VOL. 30,NO. 6
preparation of fungus-resisting paints; and control of weed erowths.
Acknowledgment The data presented in this paper represent the cooperative efforts of a number of individuals. H. L. Morrill is responsible for most of the physical data. I. Hatfield and H. R.
RELATIVE EFFECT OP SODIUM PEN'IACHLOROPEENATE AND O-NAPHTEOL AS A hXGICID3,' AGAINST Polysliclus himdus, A WOOD-DESTROYING OROANISM
GLUE PRESERVWIOS.When auiroal glues, which are protein in nature, arc dissolved in water for use, they are attacked by fungi and proteolytic bacteria which cause mildewing, liquefaction, and putrefaction, thus destroying the value of the material as an industrial adhesive. Various chemicals have been added to glues to prevent this action; zinc sulfateand phenol are examples. The chief disadvantage of these chemicals is that large quantities must be used to obtain complete preservation. Extensive laboratory and practical tests have shown that both pentachlorophenol and its sodium salt are effective preservatives for animal glues a t surprisingly low concentrations. In general, 1 part of the chemical to 400 parts of dry glue will give complete protection even under extreme conditions, and frequently even less is required. The sodium salt, particularly, is easy to apply since it can be added to the glue batch as a water solution, The desirable properties of the glue are not affected by either form of the chemical. MISCELLANEOUS USES. Other uses for pentachlorophenol and its salts include: industrial preservation of pulp and paper, starches and dextrins, gums, proteins such as casein, albumin, and gluten, leather, rubber latex, and textiles;
Hay dcveloped the application to wood preservation and sap-stain control. R. S.Shumard made the fungicidal tests and obtained the microbiological data. The miters are indebted also to Robert A. Keboe for the information on the toxicity of pentachlorophenol to rabbits and guinea pips.
Literature Cited P.,2. phwsiol. Chem., 47, 173-99 i-""",. Bendikt, R., and Scbmidt, M..Monntsh., 4,606 (1883). Erdmapn. 0. L.. 3. pa&. Chem., 22, 272 (1841); Ann.. 37,
(1) Bechhold, H.. and Ehrlich. ,IO,,*\
a43 (1841). Hubert, E. E.. Western Pine Asuoc.. Tech. Bull. 6 (1936). rev. erl (19171. ,~ Keboe, R. A., personal oommunicetione. Laurent,A,. Ann.. 48. 314 (1645). Lsurent.A., Ann. el&. phws., 131 3, 497 (1843). Meru. V., and Weith. W.. Ber.. 5. 458 (1672). Nason. H.K., 3.Am. Water W w k s Assoe.. 30.457-52 (198R\ ,~~..,. Schmitz, H., it al., IND.ENS.C H E ~ Anal.'Ed., ., 2,361-3 (1930). Schiitrcnberger, M. P., Bull. sue. chin., 4, 102 (1865). RBCEWEDMarch 28. 1838. Preaented belore the Division of Industrial and Engineering Chemistry nt the Qitb ?.leetirig of the Amsrioan Chsmicd Society, Dni1~1.Terns. 3 p d 18 to 22, Isax.
