Rosin-Modified Phenolic Resins

However, some of the resin acids in the rosin are probably changed to pyroabietic acids during the process ofmanufacture. The content of individual ac...
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INDUSTRIAL AND ENGINEERING CHEMISTRY

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axis LITERATURE CITED

(1) Bogart, M.J. P., and Brunjes, A. S., Chem. Eng. Piogress, 44, 95(2)

104 (February 1948). Carlson, H. C., and Colburn, A. P., IND.ENG.CHEM.,34, 581-9 (1942).

Vol. 43, No. 8

(3) Clark, A. hl., Trans. F w a d a y SOC.,41, 718-37 (1945). (4) International Critical Tables, Vol. 3, p. 221, New York, McGramHill Book Co., 1928. (5) Kretschmer, C. B., and \Viebe, R., J . Am. Chem. SOC.,71, 1i93-7 (1949). (6) Ihid., pp. 3176-9. (7) Rosanoff, M. A., and Easley, C. W., Ibid., 31, 953-87 (1909). (8) Scatchard, G . , Wood, S. E., and Mochel, J. M., Ihid., 68, 1960-3 (1946). RECEIVED April 14, 1950.

Rosin-Modified Phenolic Resins P. 0. POWERS1 Battelle Mernorial Institute, Colunabus, Ohio

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Rosin has proved LO be an effective fluxing agent for HE m a n y d e s i r a b l e It is unfortunate that the phenol-formaldehyde condensates. Recent work has properties of phenol-forname “pimaric acid” was shown that rosin consists of several hydroaromatic acids, maldehyde resins early sugchosen for both the dextro some of which may not react with phenolic resins. Algested their use in drying and levo varieties, for they though direct proof has not yet been given, there is much oils; Baekeland ( 1 )suggested are not geometrical isomers. evidence of chemical combination between the phenolic the use of an alcoholic soluDextropimaric acid has been resin and the rosin acid. A chroman structure of the tion of a low-stage phenolshown by Harris to differ addition product has been suggested. from abietic acid ( 6 ) in havformaldehyde resin as a proA certain amount of crohs linking between the phenoltective coating. These mateing an unsaturated group in formaldehyde condensate and two or more molecules of rials are used as baking varthe side chain. Isodextropiresin acid is required to achieie the high melting point of nishes to some extent, but maric acid differs only in the the resulting resins. This melting point is also associated their brittleness and dark r e l a t i v e positions of the with the hardness and rapid drying of finishes containing color seriously limit their methyl and vinyl groups (9). these resins. field of application. CresolIt is apparently not known -Methods of preparing various types of phenolic resiiis formaldehyde r e s i n s w e r e whether the dextropimaric are considered in this review, as are the properties of the acids add readily to phenolused with drying oils, particucommercial materials. Methods of incorporating these formaldehyde condensates. larly with tung oil, but resins in various varnishes are also outlined. these resins were also rather When rosin is heated to 250’ 0 . (Figure 2) or above, dark in color. abietic acid is isomerized I n 1916 Berend (2’) suggested the use of rosin to flux phenol-formaldehyde condenoates. to a mixture of acidb, originally termed pyroabietict :wid, The resulting resins were first produced in Germany and known which has been shown Lo cwnsist of dehydro-, dihydro-, :md in the trade as Albertols; about 1926, similar resins were produced tetrahydroabietic acid. The, yeaction is a disproportionation and in the United States. Their introduction made possible thtx can be accelerated by the addition of dehydrogenation aataI\-qts. Because all these acids are much less readily oxidized than h i e t i c “Phour” varnishes. Their use has steadily increased, and in 1949 over 2O,OOO,OOOpounds were consumed here. They have acid, the iesulting products are considerably more stable. The been widely adopted for paints, varnishes, and printing inks. acid is partly decarboxylated to a hydrocarbon. Gum and wood Other natural resins, particularly gum Congo, have also been rosin (9) also contain about 5% each of dehydroabietic and dihyemployed as modifying agents for hard resins. These resins are droabietic acids. It has apparently not been established whether the pyroabietic acids react with phenolic resins, but such acids similar in properties to the rosin-modified matrrialfi hut are lem are seldom, if ever, used in the preparation of commercial resins. widely used. HOSIN ACIDS However, some of the resin acids in the rosin are probably changed to pyroabietic acids during the process of manufacture. The structure of the acids contained in rosin ha6 been greatly The content of individual acids in various commercial romx clarified in the past 20 years, and a fairly accurate estimate of the ill vary somewhat with the hktory of the sample. Oleoresin amount of the various resin acids present in gum and wood ropin is now available (9). Abietic acid is one of the principal acids, and usually contains about 35% levopimaric acid, while the h i s h e d wood or gum rosin contains none. The abietic acid content of is the most readily isolated (Figure 1); the term has often been wood rosin, however, is somewhat higher. I n wood and gum used to signify all rosin acids. Methods for its separation have rosin, the content of maleic-reactive acids is about the aame, or been established. Levopimaric acid has a similar structure and 50 to 55% of the acids prewnt; about 5% of unsaponibble metis readily transformed to abietic acid by heating. Levopimaric ter is also present. It has not been established whether acid8 acid reacts with maleic anhydride at ordinary temperatures, other than abietic acid condense with phenol-formaldehyde conwhereas addition t o abietic acid occurs only on heating above densates. The reactivity of the fatty acids with phenolformalde150’ C. The same adduct is formed by both acids. Abietic acid hyde condensates parallels their reactivity with maleic anhydride. presumably isomerizes to levopimaric structure before addition to Rosin can be polymerized by the use of acid catalysts, such as maleic anhydride occurs. Neoabietic acid has recently been zinc chloride, sulfuric acid, and boron fluoride, to give a dimer of found in rosin by Harris (9-11) in the presenceofacids,it,likelevoabietic acid. The structure of this material has not been estabpimaric, isomerizes to abietic acid. The three acids described lished. However, it contains considerably less unsaturation than here have a conjugated diene structure; the other acids found in rosin itself and might be considered a suitable material for pherosin do not. nolic resins. Apparently it has not been so used to any grcat ex1 Present address, Pennsylvania Industrial Chemical Corg., Clairton, Pa.

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oleic acid, indicating that compounds with a single double bond may react under such conditions. However, while one third of the phenol added to oleic acid, the remaining two thirds formed polymers or decomposition products. Certain phenolic-resin condensates gel when esterified with glycerol, which is strong evidence of the presence of a dibasic acid formed by linking at least two resin acid molecules. Viscosity increase is much greater when the phenolic resin is condensed in A B I E T I C ACID

LEVOPIMARIC ACID

AGATHIC ACID

lSOAGATH!C ACID

Figure 3.

Resin Acids in Congo

the presence of rosin (16) than with materials of somewhat sin& lar structure, including hydrogenated abietic acid and a polyterpene resin. The less soluble rosin-phenolic condensates, if cured alone, cannot be dispersed in rosin, even under continued heating a t high temperatures. Hultzsch (14) has suggested the phenyl-chroman structure, which he found was formed on reaction of styrene with a phenol alcohol, for the addition product with abietic acid (Figure 4). NEOABIETIC ACID

ISODEXTROPI MAR IC ACID

Figure 1.

tent, and it is likely that the loss of unsaturation also results in a lower reactivity with the phenolic resins. The acids of gum Congo have not been so thoroughly studied as have those of rosin, but agathic acid (Figure 3) has been isolated from it. This isomerizes in the presence of acids to isoagathic acid, which possesses a hydrogenated phenanthrene Structure with one double bond. On running the gum, one of the carboxyl groups is eliminated. Apparently, it has not been established whether these acids add to phenolic condensates, although Congo-modified phenolic resins have been offered commercially.

SALIGENIN

There are workers (16) in the resin field who feel that chemical reactions do not occur between phenolic resin and rosin, and that the function of the rosin is purely that of a solvent. As no quantitative data are available, it is not possible to deny that this may be an appreciable part of the function of rosin. However, there are several good indications that reaction must occur to some extent between the phenol-formaldehyde condensates and the resin acids. An addition compound of abietic acid and a phenol alcohol has been isolated and roughly characterized (14). Sprengling (81) has recently presented persuasive evidence of the formation of a chroman from a monomethylol phenol and

I

OEHYDROABIETIC ACID

D I HYDROA81 E T IC ACID

Figure 2.

: ,1

TETRAHYDROAB IE T I C ACID

Pyroabietic Acids

OUINONE METHIDE

/ /

H EACTION OF PHENO L-FORMA LDEHYDE CONDENSATES WITH ROSIN ACIDS

J.ck

f:

on

Hesin Acids in Rosin

+u STYRENE

2 PHENYLCHROMAN

Figure 4.

Reaction of Phenol Alcohols with Styrene

Although the reaction as shown involves only one of the double bonds in abietic acid, acids with two double bonds show much greater evidence of combination with phenolic resins ; hydrogenated resin which contains one double bond shows little viscosity increase on the addition of a phenolic resin. Oleic acid with one double bond shows little evidence (12) of addition a t the double bond. The quinone methide, suggested as the intermediate formed by the dehydration of an o-hydroxybenzyl alcohol, is assumed to add to the resin acid. If this mechanism holds, it explains the adaptability of para-substituted phenols, since, with their use, the methylol groups must be ortho to the hydroxyl group. The addition of the phenolic resin structure to abietic acid alone will do little t o increase the complexity of the resin. It is essential to link two or more resin acid molecules together t o form poly-

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basic acids, to achieve a noticeable increase in melting point and viscosity (Figure 5 ) . CONDENSATION O F PHENOL AND FORMALDEHYDE

The condensation of phenol and formaldehyde has been discussed at length (8); certain properties are, however, required for condensates for use with rosin. Para-substituted phenols are often used, because they lead to resins of much lower tendency to yellow in varnish films. Alkaline condensation of the phenol and formaldehyde is usually employed to assure a high proportion of phenol alcohols. . Phenol and paraformaldehyde may be added directly to the rosin, and the condensation of formaldehyde with the phenol and subsequent addition to the rosin accomplished in one operation. This condensation, owing to the presence of rosin, must be run under acid conditions.

!ABIETIC ACID

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moles were actually combined. If the condensation proceeded largely between molecules of the phenol alcohol, one molecule of added formaldehyde should give as much effect as higher ratios, because further amounts are inevitably lost in the condensation reaction of the phenolic resin itself. However, if the condensation of the phenolic resin constituted the principal reaction, the dimethyl01 p-tert-butyl phenol should be the most reactive material, as it conceivably could add to 2 molecules of rosin. To obtain the greatest effects, a certain amount of combination of the phenol alcohols with themselves seems essential to the most viscous resins. The para-substituent in the phenol does not greatly affect the increase in melting point of the resulting condensation product with ester gum. There is a gradual decrease from methyl to benzyl group in the para position. The melting point increase with p-cresol is 50 ",whereas with terl-octyl it is only 40'. Phenylphenol condensates increase the melting point 47 '. However, the solubility increases (29) as larger groups are introduced, the tertoctyl being the most soluble of the series. Although condensates from tert-butyl phenol will give viscosity and melting point comparable to those of all the commercially available rosin-modified phenolic resins, the m e of phenols having three reactive positions results in greatly increaaed viscosities (19). In fact, if 2 moles of formaldehyde are condensed with a phenol with three reactive positions, the condensate cannot be successfully dispersed in rosin. If much smaller molar ratios of formaldehyde are used, it is possible to obtain a condensate that can be dispersed in rosin. However, by use of mixtures of a para-substituted phenol and a phenol with three reactive positions, it is possible to obtain condensates which can be dispersed in rosin to give addition products of very much higher viscosities than the commercially available resins. I n many cases, however, these highly viscous condensates cannot be esterified with glycerol, because insoluble gels are formed. Condensates have been made ranging from 25 to 67% trireactive resin (19). The materials become much more viscous and less soluble with the greater percent,age of trireactive materials. REACTION OF PHENOLIC RESINS WITH DRYING OILS

Figure 5 .

Rosin-Phenol Condensate

More uniformity is usually assured if the phenolic compound is condensed with formaldehyde under controlled conditions, and later reacted with the rosin. On condensation of 2 moles of formaldehyde with p-tert-butyl phenol, the melting point of the condensation product with rosin varies somewhat with the degree of condensation of the phenolic resin. If the resin is stopped either as a highly viscous liquid, or as a low-melting resin, it will increase the melting point of ester gum about 46' C. If, however, the resin is heated further to a melting point around 150" C., the melting point of the condensate with rosin drops progressively until only 14" increase is noted. This probably represents the full effect of the resin when combination with rosin does not occur ( I S , 16). The increase in melting point follows the increase in amounts of formaldehyde ( I S ) . If 0.8 mole of formaldehyde per mole of tert-butyl phenol is employed, the increase in melting point is IS", comparable to that obtained with the higher melting condensate using 2 moles of formaldehyde. As the molar ratio of formaldehyde is increased to 2 moles, the melting point increase rises to 46" C. Further increase in the amount of formaldehyde results in no further elevation of the melting point of the condensate with ester gum. I n fact, no great increase is found after 1.6 moles of formaldehyde are employed. The use of 2 moles of formaldehyde does not necessarily assure the combination of that amount; it may be that, with 2 moles of formaldehyde used, about 1.5

The combination of phenol-aldrhyde condensates with the drying oils has been studied by many investigators (3,4,I d ) , and there is still considerable doubt as to the extent of combination of these resins with the drying oils. Some of the arguments suggested above for the combination of methylol phenols Kith rosin would also indicate a combination with the drying oils. It would appear that the conjugated acids combine ( I d ) much more readily than the nonconjugated variety, as linseed oil increases in viscosity only three times when dimethylol butyl phenol is added and nearly seven times when dehydrated castor oil is used. The softer liquid resins give much more increase in viscosity than do the same materials when heated to advance the melting point to 150" C. In this case, the increase in viscosity is about twice that of the original oil, which indicates that there is but slight chemical reaction with linseed oil. I n working with the methyl esters of palmitic, oleic, linoleic, and oleostearic acids, it was found that dimethyl01 p-cresol showed no evidence of combination with the palmitate or the oleate a t the double bonds. Some transesterification occurred, but this reaction did not proceed far; with rosin, the reaction apparently does not occur at all (12). The results are not capable of interpretation on a quantitative basis, as the esters were recovered b y distillation and the more unsaturated esters may have been bodied in the treatment. However, it seems clear that a certain amount of combination of polyunsaturat~dacide with methylol phenols occurs. It is a little hard to explain the lack of reactivity of oleate esters in view of the suggested phenyl-chroman structure. As with the resin acids, phenolic bodies seem to react more readily with the acids or esters that react readily with

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maleic anhydride. It has been suggested that use of acid catalysts (17) promotes the combination of phenolic resins with drying oils, and that boiled oils react somewhat more readily with phenolic resins than does raw linseed oil. However, tung oil apparently combines very much more readily. MANUFACTURE

Resins are usually made by condensing formaldehyde with B para-substituted phenol. In some cases, the para-substituted phenol may be bisphenol, which has the properties of a trireactive phenol. However, if a deficiency of formaldehyde is used, it may have the behavior of a para-substituted phenol. After the condensation has been carried to the desired viscosity, the material is usually added to rosin a t temperatures up to 250"C., to complete the reaction of the phenol alcohol. The polylol, usually glycerol, is then added, and the material is heated for several hours a t 280" C. or above until acid values below 20 are reached. Inert atmospheres are used t o protect the color of the resin. Application of a vacuum increases the molecular weight and raises the melting point of the resin. This may be due t o removal of the volatile decomposition products of rosin, and t o promotion of further esterification. The resins are poured and broken up into lumps. COMMERCIAL RESINS

.

PHENOLIC SIRUPS. Recently, phenolic sirups have been offered for use with rosin. These can be reacted with rosin and subsequently esterified; the resulting resin can be dispersed in drying oil. The rosin-phenolic adduct can be formed and dispersed in oil, and the mixture esterified. This method (19)works satisfactorily with viscous resins which would gel if esterified with glycerol alone. Twelve per cent of one of these sirups will raise the melting point of the glyceride to approximately 135" C., and the other sirups which give somewhat more soluble condensates will raise the softening point to 115" C. Hard resins have also been supplied for use with rosin ester gum. MODIFIEDESTERS. The many yarieties of rosin-modified phenolic resins available on the market vary with the rosin used, in the phenolic content, in the types of phenols used, and possibly in the ratio of phenolic to formaldehyde. Both gum and wood rosin are used for commercial resins, and tall oil has been used as a aource of rosin for producing modified resins. The resins fall roughly into soluble and insoluble grhups, although no quantitative test for solubility has been generally adopted. A variety of polylols have been used. Glycerol is probably much more generally employed than other materials, but in recent years several modified phenolic resins, in which pentaerythritol has been used, have been offered on the market. Some of the Albertols' (6) have been formed from 2,2'-bie(p hydroxypheny1)-propane, which is dissolved in 2 moles of caustic soda and reacted with 4 moles of formaldehyde. The reaction mixture is cooled, neutralized, and washed with water and the condensate is then heated until a semihard resin is formed. One hundred parts of rosin are heated with 15 parts of the above resin, and the product is esterified with glycerol. The esterification is continued until the acid value is below 20. Comparison of competitive commercially modified resins is not always simple, because each manufacturer seems to prefer his own test methods. Melting point, for instance, is determined by the ball and ring method, the capillary tube method, the mercury method, the drop method, and the heated-bar method. Viscosities in solution in an aromatic hydrocarbon are used by several manufacturers, although there is no agreement on the concentration of the resih. Viscosities in solution and the melting points, in general, increase together, but do not always show a close correlation. This might be expected (7), because the melting point is much more likely to be affected by the lower molecular weight material present, while the viscosity is more likely to be

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influenced by higher molecular weight materials. To describe the color of the resins, some use the rosin-color standards and others various color standards of solutions of the resins. Some resins consist of the rosin-phenolic condensate which ha8 not been esterified. Such resins have a high melting point and excellent hardness. Many of the low-melting resins are characterized by a relatively low content of phenolic resin. These materials melt from 115" to 135" C., as determined by the ball and ring method. A majority of the resins melt in the range of 140' t o 160" C. by the ball and ring method. Comparatively few resins are available which have melting points from 160' t o 180 C.; their acid values, in general, are between 10 and 20. There is, however, a trend for the higher melting resins to be somewhat higher in viscosity than the softer resins. There is not too much difference in color, but the softer resins are, in general, lighter in color. Many of the modified phenolic resins are developed for use with either tung oil or linseed oil, the requirements being rather different for each oil. The solubilities of the resins are, perhaps, best indicated by the temperature a t which they will dissolve in the drying oils. Some of the softer resins can be dispersed in the drying oils as low aa 175" C.; the more soluble resins, melting in the middle range, can be dispersed a t approximately 230' C. Some of the less soluble resins and the resins in the higher melting and'more viscous ranges may require temperatures as high as 275" C. for complete dispersion. Solubility is also measured by tolerance for mineral spirits. Many of the softer resins are soluble in all proportions; the materials in the medium melting point range are precipitated on the addition of 4 to 6 parts of mineral spirits, and the least soluble resins often will not stand dilution with 2 parts of mineral spirits. It has recently been shown (18) that, in the absence of phenolic reeins, it is necessary to reduce the conjugated triene in oil to B very low figure to make the oils gasproof. However, in the presence of phenolic resins, it is possible to achieve gasproofing properties when an appreciable amount of conjugated triene is present. The amount and type of phenolic resins used in the reaction with rosin in the formation of modified phenolics, used in the preparation of commercial resins, have, in general, not been described. However, in most cases, between 10 and 20% of phenolic resin is sufficient to give commercially usable resins. O

UTILIZATION OF RESINS

These resins are used in printing inks and in varnishes, with either linseed oil or tung oil. In general, the highest melting resins cannot be used with tung oil, as they can be dispersed only a t high temperatures a t which the oil would gel. They cannot be used t o chill the oil, because they require considerable time to dissolve. Several resins have been developed for use with tung oil. These may have a higher phenolic content and somewhat higher acid number, both factors decreasing the rate of bodying of the tung oil. The modified phenolic resins enter into ester interchange (10)during the process of heat bodying, and the rosirm acid groups enter into the oil structure. Varnishes of good drying properties and good water resistance are obtained by the use of modified phenolic resins. Some of the less soluble resins cannot be dispersed in large to equal weights of amounts of drying oils, but, if heated with linseed or other drying oils, they may be dispersed. The varnish so formed can be diluted with further amounts of oil and the cooking continued. LITERATURE CITED

(1) Baekeland, L. H., J. IND. ENG.CHEM.,3, 938 (1911). (2) Berend, L., U. S. Patent 1,191,390 (July 18, 1916). (3) Brown, K., Ibid., 1,212,738 (Jan. 16, 1917). (4)Byok, L. C., Ibid., 1,509,079 (June 22, 1926).

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INDUSTRIAL AND ENGINEERING CHEMISTRY

(6) DeBell, Goggin, and Gloor, “German Plastics Practice,” Springfield, Mass., DeBell and Richardson, 1946. (6) Fieser, L. F., “Katural Products Relative to Phenanthrene,” 3rd ed., New York, Reinhold Publishing Corp., 1949. (7) Flory, P. J., “Effect of Molecular Weight on Physical Properties,” Division of Paint, Varnish, and Plastics Chemistry, 117th Meeting, Anr. CHEM.,SOC., Detroit, April 1950. (8) Fonrobert, E., Pette u. Seifen, 50, 514 (1943). (9) Harris, G . C., J . Am. Chem. Sac., 70, 3671 (1948). (10) Harris, G. C., T a p p i Monogrnph Ser., No. 6, Appleton, Wis., September 1947. (11) Harris, G. C., and Sanderaon, T. F., J . Am. Chem. SOC., 70, 334 (1948). (12) Hilditch, T. P., and Smith, C. J., J . SOC.Chem. Ind., 54, 1111 (1935). (13) Honel, H., J . Oil Colnw Ciicn. Assoc., 21, 247 (1938).

Vol. 43, No. 8

(14) Hultzsch, J., J . prakt. Chem., 158, 275 (1941). (15) Krumbhaar, W., “Coating and Ink Resins,” New York, Reinhold Publishing Corp., 1947. (16) Krumbhaar, W., U. S.Patent 2,478,490 (Aug. 9, 1949). (17) Mazzucchelli, A. P., Ibid., 2,413,412 (Dec. 31, 1946). (18) Oswald, F. G., Oficial Digest Federation P a i n t &: Varnish Product i o n Clubs, KO. 608, 625 (1950). (19) Powers, P. O., IRD.ENG.CEIEM., 36, 1008 (1944). (20) Ibid., 42, 146 (1950). (21) Sprengling, G., Division of Paint, Varnish, and Plastics Chemistry, 118th Meeting, AM. CHEM.Soc., Chicago, September 1950. RECEIVEDSeptember 23, 1960. Presented before the Division of Paint, Varnish, and Plasticfi Chemistry a t the 118th Meeting of the AUERICAN CHE\IIC4L SOCIETY, Chicago, 111.

Autoxidation of Hydrazine J

EFFECT OF DISSOLVED METALS AND DEACTIVATORS L. F. AUDRlETH AND P. H. MOHR W . A . Noyes Laboratory of Chemistry, Unii:ersity of Illinois, Urbuna, I l l . Interest in the use of hydrazine as a specialty hydronitrogen fuel has made necessary a study of the stability of this substance, as both the aqueous and highly concentrated material, toward deterioration by atmospheric oxygen. Hydrazine undergoes autoxidation with the intermediate formation of hydrogen peroxide and eventual decomposition to nitrogen and water. This reaction is catalyzed markedly by dissolved copper. Metal deactivators which form very insoluble salts or stable complexes with copper can be employed as inhibitors. The more effective stabilizers include sulfide (added either as soluble sulfide or as elemental sulfur), Seques-

trene AA, dithizone, thiocyanate, potassium ethyl xanthate, p-tert-butylcatechol, and sodium diethyl thiothionophosphate. Polyamines are usable in dilute aqueous hydrazine, but are relatively ineffective in the highly concentrated material. It is recommended that 3 to 5 p.p.m. of the more effective deactivators be added to overcome the catalytic effects of any copper that may be introduced during the storage, shipment, and handling of hydrazine. Elimination of copper and copper alloys in equipment or apparatus designed for the manufacture, storage, handling, or use of hydrazine is desirable.

ONSIDERATZON of hydrazine as a specialty fuel has posed a number of problems with respect t o its stability during manufacturing operations, handling, storage, and use. Not only is hydrazine subject to catalytic decomposition by a number of active metals, specifically by nickel and cobalt ( I ) , but it also undergoes reaction with molecular oxygen. Such autoxidation of hydrazine results in deterioration of the product and loss in strcngtla both in dilute aqueous solution and in highly concentrated hydrazine. Although it was definitely proved by Cuy and Bray (4)that hydrazine reacts with molecular oxygen, no quantitative study of this phenomenon was made until Gilbert (6) and his students undertook to investigate autoxidation in dilute aqueous solution. Gilbert found that the autoxidation of dilute aqueous hydrazine always leads to the formation of some hydrogen peroxide as an intermediate, but that the over-all reaction yields nitrogen, water, and traces of ammonia; that the reaction is heterogeneous in nature; and that the rate of the reaction depende on the surface area of the solution, the partial pressure of oxygen above the solution, and the hydroxyl ion concentration. These observations were subsequently verified by Brown ( 2 ) in this laboratory and extended from the very dilute solutions employed by Gilbert (0.25 M ) to approximately 1 M solutions. Brown also established the fact that traces of copper exert a marked catalytic effect on the autoxidation of hydrazine, Actually, the dissolved copper content of distilled water, less than 0.5 p.p.m., greatly accelerated the autoxidation of dilute aqueous solutions. The experimental work presented below demonstrates that such autoxidation of hydrazine is markedly and uniquely catalyzed by dissolved copper; and that materials Fhich reduce the con-

centration of dissolved copper can be added to inhibit tlic catalytic effect, thus stabilizing both dilute and highly concentrated solutions of hvdrazine against deterioration and losa of qtrength. PROPERTI’ES OF HYDRAZINE

The physical properties of anhydrous hydrazinc are given in Table I. Hydrazine has a liquid range which is comparable to that of water, it has a relatively high density as compared with other fuels, especially hydrocarbon-type fuels, and its heat of combustion is high. The combustion products are nitrogen and water, whose average molecular weight is low compaied with products obtained when hydrocarbon fuels are used. Hydrazine is furthermore an endothermic compound, which factor contributes t o the energy value of hydrazine as a fuel but is, in part, an objectionable feature, as exothermic decomposition once initiated can be made to proceed most rapidly.

TABLE I. PROPERTIES OF HYDR~ZISE Melting point Boiling point , Density Heat of fusion Heat of vaporization Dielectric constant Heat of combustion

20 c. 113.5O C. (1 atm.) 1.014grams per cc. (15’ C.) 3 . 2 kg.-cal. per mole 10.7 kg.-cal. per mole (25“ C . ) 61.7 (25’ C.) 148.6 kg.-cal. per mole

The chemical properties of hydrazine must also be borne in mind during the handling and use of the material. Hydrazine is a powerful reducing agent and will effect reduction of many oxides, hydroxides, and compounds of the less active