when ruptured at -150" F. This applies to both cast and forged or rolled parts. A steel of the following type has been found suitable for making valve castings which, when heat-treated in accordance with the outlined procedure, will give Charpy values averaging around 20 foot-pounds and excellent tensile values as well. It can be cast into intricate forms, such as valve bodies and bonnets, without great difficulty, and it compares in cost favorably with ordinary alloy steels of high quality. A typical chemical analysis of this steel and its physical characteristics follows: Chemical Compn., yo Carbon 0.08 Manganese 0.29 Silicon 0.12 Phosphorus 0.015 Sulfur 0.018 Nickel 4.06 Vanadium 0.16 Molybdenum 0.50
Physical Characteristics Tensile strength, lb./sq. in. 1L07,OOO Yield point, lb./sq. in, 88,000 Elongation, % 22.5 Reduction of area, yo 61 Brinell hardness 200 Charpy impact resistance a t - 150' F., ft-lh. 20.6 Heat Treatment Heat to 1800-1850" F Cool in air Reheat to 1550' F. Quench in oil Draw to 1250' F.
Mannitol and
Sorbitol R. MAX GOEPP, J R . , AND ~ K. R. BROWN Atlas Research Laboratory, Tamaqua, Pa.
T
For bolts, studs, and other trim used in the construction of valves, a bar stock material such as S. A. E. 4140 steel with the following approximate specifications will give satisfactory results : Chemical Compn., yo Carbon 0.40 Manganese 0.70 Silicon 0.22 Chromium 0.95 Molybdenum 0 . 2 0 Phosphorus 0.016 Sulfur 0.018
Resins from
Physical Characteristics Tensile strength, lb./sq. in. 130,000 Yield point, Ib./sq. in. 105,000 Elongation, yo 21 Reduction of area, yo 58 Brinell hardness 238 Charpy impact resistance a t -- 150' F., ft-lb. 18.3 Heat Treatment Heat to 1575' F. Quench in oil Draw to 1275' F.
Sometimes it may be desirable to surface-harden parts of the equipment in order to reduce the chances of galling where such parts are in sliding contact under high pressure with other parts of the same metal. In this case such parts may be surface-hardened by a carburizing treatment. Numerous tests have been made to determine whether there would be a tendency to spalling off of the hardened surfaces a t subzero temperature. These tests indicated that this would be extremely unlikely if the thickness of the case is not excessive. Where plug valves of the pressure-lubricated type are installed, suitable lubricants must also be used. They are available in several varieties with satisfactory characteristics a t low temperatures and are suitable for resistance against various solvents. They are generally applied by means of pressure guns and lubricant nipples. These lubricants offer a valuable means of preventing galling and seizing of the soft metal valve surfaces, and they are also extremely effective in sealing the valves against leakage of the high vapor-pressure fluids entering into these subzero processes. I n view of the likelihood of the extension of processes involving the use of extremely low temperatures and high pressures, it would appear that alloy steels of high impact resistance a t these temperatures will come into more frequent use. RECEIVFOD July 28, 1938.
HE hexahydric alcohols, mannitol and sorbitol, as polyfunctional bodies are capable of forming resins with polybasic acids or with resinous monobasic acids. Such resins derivable from the hexitols include the alkyd or phthalate, the succinate, maleate, adipate, the citrate mentioned by Hovey (6),the oil-acid modified alkyd, and the ester gum from rosin. Previously it has been generally assumed that all 6 hydroxyl groups of mannitol and sorbitol are reactable in resinous esterifications (3,6 ) . In 1930 Kienle ( 6 ) published data on a mannitol-phthalate resin made with 6 acid equivalents, and showed that the product had a higher flow point and poorer moisture resistance than the corresponding glycerol resin; he drew the inference that "the cause of the decrease in water resistance is undoubtedly due to the presence of uncombined hydroxyl groups which are necessarily more numerous the greater the reactivity of the alcohol molecule, as earlier gelation blocks their combination." A few preliminary experiments on modified alkyd resins soon demonstrated that the ordinary glycerol technic was not suitable, and that the course of the reaction was apparently different, since, using acid equivalents equal to about threefourths of theory, the hexitol resins had acid numbers of 106 to 138, compared to glycerol resins a t 20 to 30. It was suspected that inner ether formation, according to the equation, CsH*(oH)e-----f CsHsO(0H)r
was taking place, and that in effect, only 4 instead of 6 hy-
droxyls were available. Accordingly, the acid ratio was cut in half and the acid numbers of the hexitol resin were brought down to 50. The inner ethers of the hexitols are the tetrahydric or dihydric, mono- or dianhydro products, having the empirical formulas CBHsO(0H)d and CsHsO,(OH),, obtainable from the hexitols by intramolecular loss of one or two moles of water 7). under various conditions (4, Later a more extensive investigation of hexitol resins showed that, with ester gums, the optimum ratio of rosin to hexitol was 5 to 1 by weight, or about 2.76 acid equivalents. This would be (2.76/4.00=) 0.69 of theory for the inferred tetrahydric inner ether. Since the observed effect might have been due to steric hindrance or diminished reactivity of hexitols compared to glycerol, the inner ether hypothesis was further tested by substituting a mixture of preformed sorbitol inner ethers, or sorbitans, for the sorbitol a t the same acid ratio. The sorbitan 1
1222
+ H,O
Present address, Atlas Powder Co., Wilmington, Del.
NOVEMBER, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
resin obtained was virtually identical with the corresponding sorbitol resin. Finally, direct evidence was elicited by saponifying both the sorbitan and sorbitol resins, and identifying in the watersoluble residue from both and in the mixed sorbitan starting material, the same individual monoanhydrosorbitol (or sorbitan). Isolation and identification were accomplished by means of the di-m-nitrobenzal derivative. The study of hexitol resins was then extended tooil-acidmodified alkyd resins, made a t 200" C., instead of at 250-300" C., the temperature used for ester gums; here again the sorbitan inner ether was found in the polyhydroxylic saponification residue. The resins were reproduced on a larger scale and tested in varnishes and other coating compositions against laboratoryproduced corresponding glycerol resins and accepted commercial resins. When saponified the glycerol resins yielded only glycerol. From the experimental work reported here on the preparation, performance, and composition of resin esters and phthalic amhydride-linseed oil resins from hexitols, it is concluded that: 1. The functionality or react,ivity of hexitols in high-temperature resinous esterification is not 6, and no more than 4,owing t o inner ether formation. Evidence for this is fourfold: a. Chemical identification of a t'etrahydric monoanhydrosorbitol or sorbitol inner ether in the polyhydric residue recovered by saponification from sorbitol resins. b. The substantial identity of rosin ester gums (Table VII) prepared from sorbitol and from amixture of tetrahydroxy monoanhydrosorbitols. c. The similarity between glycerol resins and sorbitol resins made at the same ratio of acid to hydroxyls, calculated on a basis of 4 and not 6 hydroxyls for the sorbitol (Table 111). d. The decided increase in acidity of sorbitol resins in passing from 4 acid equivalents per mole of original hexitol to six equivalents (Table 111). 2. The modified alkyd resins and ester gums from hexitols are substantially equal to corresponding glycerol resins in moisture resistance, and superior in several other technical aspects. 3. The optimum ratios of acid equivalents per mole of hexitol are 3 for linseed oil-phthalic anhydride resins and 2.76 for rosin ester gums. 4. The rake of polymerizing condensation for hexitols is slower than for glycerol in linseed oil-phthalic anhydride resins.
Technic of Resin Preparations For several reasons the technic required to produce satisfactory hexitol resins is more exacting than that for glycerol resins, because of the qualitative and quantitative differences in the behavior, under esterifying conditions, of the trihydric and hexahydric alcohols. Thus, whereas for glycerol 2.5-3.0 equivalents of acid per 3 hydroxyls are preferred, for hexitols only 2.25 to 3 acid equivalents per 6 hydroxyls should be used. I n other words, the preferred stoichiometric acid-hydroxyl ratio is 0.75-1.0 for glycerol and only 0.38-0.50 for hexitol. Intimate contact between the polyhydric alcohol and the esterifying acid, particularly rosin, is harder to achieve with the hexitols than with glycerol, because of the higher viscosity, greater density, and more pronounced lyophobe character of the hexitols. Accordingly, stirring must be extremely thorough, since convection currents and steam bubbles are not enough to keep the reactants in satisfactory contact during the earlier stages of the reaction. Stirring is also necessary to prevent local overheating since the thermal decomposition products of hexitols are much deeper in color than those of glycerol. (The hexitols do not decompose to acrolein.) This thermal decomposition is accelerated by metallic impurities, particularly the alkalies, alkaline earths, and iron. Aluminum and its more common alloys are without apparent effect. Air must be excluded in the interest of color.
1223
Satisfactory ester gums and alkyds can be made from mannitol and sorbitol by using from 2.25 to 3 acid equivalents per molecule of hexahydric alcohol, and by controlling purity of ingredients, heating schedules, agitation, and atmosphere. Ester gums thus prepared a t 285-300 C. have acid numbers below 20, standard rosin colors G to H, and softening points between 120 and 140' C. (ring and ball), with properties intermediate between glycerol ester gums and modified phenolic types. When air-drying alkyds from sorbitol at 200-225" C. are tested in synthetic enamels and baking enamels they compare favorably with corresponding glycerol resins and surpass the latter i n resistance to cold check, salt spray, humidity, and hydrocarbons. The saponification of certain sorbitol alkyds or ester gums yields qualitatively a tetrahydric monoanhydrosorbitol or sorbitan, CGH8(0H),0, isolated as a di-m-nitrobenzal derivative (melting point, 194" C.); this sorbitan can be isolated in the same way from the monoanhydrosorbitol fraction (boiling at 235-250" C. at 3 m m . ) , made by heating sorbitol with mineral acids. From the saponification of glycerol ester gums and alkyds, only the original polyhydric alcohol can be recovered. The fact of internal etherification therefore explains the qualitative and quantitative differences between hexahydric and lower polyhydric alcohols i n the formation of resinous esters.
,
Preparation and Testing of Ester Gums from Hexitols Mannitol and sorbitol are added as dry powders, or the sorbitol may be in the form of concentrated aqueous sirup containing about 15 per cent water. Commercial mannitol is a c. P. product, but various grades of sorbitol are available, and a grade sufficiently low in ash and sugar must be used where color is of importance. The kettle should be closed and provided with stirrer and means for applying either vacuum or inert gas jetting, preferably both. The heating-up schedule should be slow to prevent overheating. A rate of 1' C. rise per minute, after mixing the ingredients a t 120' C., is satisfactory. The final temperature should be 285-300' C. Above 300' C., the gain in reaction rate does not compensate for loss in color; a t 250" C. the reaction is considerably slower. By using lower ratios of rosin to hexitol, it is possible to make resins of low acid number without allowing anything but water or readily volatile by-products to escape from the reaction mixture; but the most useful hexitol ester gums are obtained by employing a 5-1 rosin-hexitol ratio by weight, and distilling or jetting off the lighter rosin oils and acidic byproducts from the reaction mixture. Table I gives data on typical rosin-hexitol resins made under various conditions. I n converting ratios by weight to acid equivalents of rosin per mole of hexitol, the technical WW rosin used is assumed to have an equivalent weight of 320.
The resins in part A of this table were reacted and jetted to an approximately constant acid number, using a stream of carbon dioxide. I n part B, resins made under the same conditions, but without jetting, are shown for comparison.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1224 ~~
~
~~
~
~~~
TABLEI. HEXITOLESTERGUMS MADE AT VARIOUSRATIOS Expt.
No.
Hexitol
1 2 3 4 5 6
Sorbitol Sorbitol Sorbitol Mannitol Sorbitol Sorbitol Sorbitol
7
Acjd Wt. EquivaYield, Ratio lents er MoE Hrs. a t Ori%al Rosin) Hexitol Hexitol 300' C . Solids A . Resins Jetted
3.6-1 5-1 5-1 5-1 6.5-1 8.3-1 11-1
2.0 2.76 2.76 2.76 3.6 4.6 6.0
3.0 3.0 3.0 3.0 6.5 5.25 5.25
77 72 66 66 68 55 46.5
Acid No.
Color4
Softening P2int.b
C.
111
16
118 129 133
B. Resins Not Jetted 2.76 3.0 Sorbitol 5-1 87 20 84 (E-F) 102.5 4.6 Sorbitol 8.3-1 3.5 95 50.5 60 (F-G) 102 6.0 Sorbitol 11-1 5.25 85 70 40 (.H.) 100 a On this scale the standard rosin types have the values F = 70,G = 50,H = 36,as measured in 50 per cent toluene solutlon in the Hess-Ives colorimeter. b Ring and ball. 8 9 10
Since the yield is determined by the duration and strength of the jetting, it is obvious that the same yield can be achieved by stronger jetting for shorter periods or milder jetting for longer time. The jetting varied somewhat in the resins of part A so that yields and times are not strictly consistent for the examples given. However, for the data presented, which may be taken as typical for acid numbers near 20, the following may be noted: The color is somewhat off at the lowest ratio; otherwise it is not affected much by time or jetting, and ranges between G and H. The softening point varies inversely as the yield, but the correlation is not perfect, since, as experiments 3 and 5 (Table I) show, resins differing only 2 per cent in yield and one unit in acid number have softening points 8" C. apart (122" vs. 114°C.); on the other hand, resins 1 and 5, differing by 9 per cent in yield and made with widely different ratios, have softening points only 3" C. apart. However, as resins 1 or 8 and 7 show, wide differences in ratios and yields a t a constant acid number can lead to wide differences in softening point, amounting to some 30°C. The effect of jetting is shown by comparing resins 8, 2, and 3 where a t the same ratio, time, and acid number the softening points vary from 102.5" to 122' C. and yields from 87 to 66 per cent. The yield a t a given ratio and reaction time varies with the jetting, as resins 8, 2, and 3 show. With increasing ratio at constant acid number the yield must be decreased, until with the supposedly theoretical stoichiometric 6 equivalents the yield is less than 50 per cent. The reaction time must be increased with ratios above 2.76 to obtain an acid number of 20, with no significant advantage from the standpoint of color, softening point, or yield. Mannitol is equivalent to sorbitol. On the basis of color and reaction time, the preferred ratio is 2.76 acid equivalents per mole of hexitol. Vacuum distillation has substantially the same effect as inert gas jetting. Rosin reacts with polyhydric alcohols very slowly below 240" C., and it decomposes at 300" C. Hence, although the bulk of the esterification may be completed during the hour taken to pass from 240" to 300" C., considerable chemical change takes place, involving both the residual unreacted rosin and whatever rosin ester has been formed during the subsequent heating a t 300". Also, in jetted or distilled resins part of the acidity is removed as acidic distillate. Accordingly it is impossible to discuss these so-called ester gums from a strictly stoichiometric standpoint. The color, acid number, and softening point of the typical hexitol ester gums rank them more with the phenol-aldehyde modified ester gums than with the ordinary very pale, almost neutral, and softer glycerol ester gums.
TABLE 11.
VOL. 30, NO. 11
Four resins were made a t a ratio of 2.76 to 1, with acid numbers of 13 to 21 and softening points ranging from 100' to 122" C., at corresponding yields of 81 to 61.5 per cent. These four resins were then compared with a standard commercial resin of the phenol-aldehyde-ester gum type in a synthetic white enamel, which was sprayed on furniture steel, aged 10 days a t room temperature, and then tested for resistance to humidity, salt spray, ultraviolet light, and outdoor exposure. The sorbitol resin made a t highest yield and lowest softening point was the best of the four. The comparison between it and the standard commercial resin is given in Table 11. The sorbitol resin is thus the equal of the commercial resin, in this particular application, in all but resistance to chalking. The moisture resistance is quite satisfactory. COMPARISON OF SORBITOL ESTERG u M 4 AND COMMERCIAL RESININ SYNTHETIC ENAMEL
--Appearance of Test PanelAdhe- BlisDis-' Resin Test sion ter Rust Chalk color Sorbitol Humidityb Good None . . . .... ... Standard Good None . . . .... ... Sorbitol Salt sprayc Fair . . None .... Standard Fair . . . None ... ... Sorbitol Ultravioletd Good . . . . . . Considerable Some Standard light Good . . . .. . Slight Some Sorbitol Outdoor exposure# Fair ... ... Slight Some Standard Fair . . . . . Very slight Some Ratio, 2.76-1; yield, 81 per cent: acid No., 21; color, 40; softening point, looo C. 98 per cent relative humidity a t 43" C. for 80 hours. 0 5 per cent NaCl solution smaved a t 15-21' C. for 60 hours. 18 inches from IO-inch UGarc tube for 50 hours. * South exposure test fence, 60' angle, Chicago, July-August, 1934, 55 days.
.
.
...
.
Air-Drying Alkyd Resins from Hexitols The methods used for producing modified alkyd resins from hexitols are substantially the same as for the rosin gums, in so far as purity of ingredients, desirability of vigorous agitation, and exclusion of oxygen are concerned. A final reaction temperature of about 200" C. is preferred, however. The same heating-up schedule of 1' C. per minute rise is satisfactory. Whereas with ester gums, resins of low acid number can be made a t a severe cost in yield by starting with the supposedly theoretical stoichiometric six equivalents and removing excess acid during the reaction by jetting or vacuum distillation, this cannot be done with dibasic acids. Gelation takes place before the excess acid can be removed, and the resulting resinous mass contains much combined acid as acid ester, as well as considerable unreacted dibasic acid. Table I11 shows results with typical linseed oil-phthalic anhydride-sorbitol resins, in which the oil-acid content was kept a t 30 per cent by weight of the original reactants, while the total acid ratio was varied from 1.75 to 6 equivalents. Corresponding glycerol resins a t 1.75, 2.25, and 3.0 equivalents are shown for comparison. The "ratio, acid equivalents to reacting hydroxyls" in the first column is calculated on the assumption that the sorbitol is converted completely to tetrahydroxy monoanhydrosorbitoll while the glycerol is unchanged. The following conclusions may be drawn: 1. The useful sorbitol resins are made at acid equivalents of 2.25 to 4.0. At 1.75 drying does not occur, and at 6.0 excess unreacted acid is present.
NOVEMBER, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY
1,225
3
These resins were tested in synthetic enamels, lacquer enamels, and wood lacquers. In preparing the synthetic Ratio, acid equivalents t o reactenamels, 18 ounces of the 15 per cent ing hydroxyls 0,4375 0 , 5 6 2 5 0.5833 -0.751.OO1.5 Polyhydric alcohol Sorbitol Sorbitol Glycerol Sorbitol Glycerol Sorbitol Glycerol Sorbitolb Of the resins were 5-1.75 S-2.25 G-1.75 S-3 G-2.25 S-4 . G-3 s-6 ground with 24 ounces of titanium oxide Sample No. Acid equivalents/ and 12 to 13 ounces of solvent naphtha; mole alcohol 1.75 2.25 1.75 3.0 2.25 4.0 3.0 6.0 then the pastes were let back with 'an Hr. at 200' C. to Nongel gelling 28 >24 20 18 2 6 5 16 equal weight of the resin solution. Two Hr. at 200' C. for test 20 22 15 18 18 22 4 16 series of enamels were made. The first, Acid No. 3 7 < 1 24 4 46 47 'lo without drier, was made as described 70 5 >48 4 5 3 3 NonDrying time, hr. drying and used in testing drying time in air Comparative viscosity, sec. 30 135 35 130 (220) 120 200 ... and also for baking tests. The other contained as drier 0.1 per cent cobalt 0 Drying time t o tack-free condition from 50 per cent toluene solution, on brass at 20-25" C.; viscosity, time h efflux, in seconds of 50 per cent toluene solution, from a 10-ml. pipet at 1-85 per cent lead, based on dry and 25' C . b Excess unrertcted phthalic anhydride in finished resin. resin. This enamel was used only for testing air drying with a drier. The enamels were sprayed on furniture 2. The %equivalent sorbitol resin, though inferior to the 4steel, and were tested after air drying and after baking one equivalent in drying time, is much less acid. hour each a t 150°, 200°, 275", and 300" C . (without 3. When sorbitol and glycerol are compared at equal aciddrier)* hydroxyl ratios, assuming that the sorbitol reacts as tetrahydric monoanhydrosorbitol, they are quite similar at acid-hydroxyl ratios of 0.75 and 1.00. At 0.75 (samples S-3 and G-2.25) and TABLE IV. SORBITOL the same time of reaction, the sorbitol dries somewhat faster, is AND GLYCEROL ALKYDS USEDFOR TESTING somewhat less viscous, and is much more acid. Gelling time is approximately the same. At a ratio of 1.00 (samples 5-4 and Acid Hours Viscosity4 G-3), the true stoichiometric for both, glycerol gels much faster Resin Equivaat Acid at 25' C., and is somewhat more viscous, but the acidity and drying time No. Alcohol lents 200° C. No. Color Centipoise8 are the same for both. However, at a low ratio of 0.57 the sorbiS-2.25 Sorbitol 2.25 24 8 116 (E) 700 to1 resin is much superior in drying time and only slightly inferior s-3 Sorbitol 3 16 3.5 50 30 22 83 (E-F) K) 300 G-3 Glycerol 3 400 in aciditly. Despite its higher functionality (4 us. 3), sorbitol G-2.25 Glycerol 2.25 16 4 14 [L) 1000 reacts more slowly than glycerol.
TABLE111. SORBITOL AND GLYCEROL LINSEEDOIL-PHTHALIC ANHYDRIDE RESINS' AT VARIOUS RATIOS(SMALL-SCALE PREPARATION)
a
For larger scale testing in lacquers and enamels, larger batches of the two sorbitol resins S-2.25 and 5-3 and the two glycerol resins G-2.25 and G-3 were made up in order to give a performance comparison of glycerol and sorbitol at the same acid-hydroxyl ratio of 0.75. They were reacted close to the gel point. Data are shown in Table IV.
Measured in 50 per cent toluene solution.
Figures 1 to 3 show the comparative behavior of four resins in the synthetic enamel tests. The range in performance extends from A+ to D-. I n the humidity and salt spray tests A+ is no blister and Derfect film, A is small uniform blister, B is Gedium blister, C is large blister; and D is flaking of fdm off the panel. These thirteen grades are plotted vertically, in the sixteen individual test plots shown, against the drying conditions-namely, drying in air without drier, air drying with drier, and baking a t 150" to 350'. The air-dried and the baked tests are grouped separately. Relative performance may be gaged at once by the relative darkness of the individual test plots. Charts of this type are convenient in h r ULTRA VIOLET HUMIDITY SALT SPRAY WEATHER spotting apparent correlations. Thus, weather resistance does not correlate with either humidity or Uviarc resistance, but apparently it does with alcohol resistance. Similarly, oil and grease resistance appears to be unaffected by baking. Sorbitol a t 3 is superior to sorbitol at 2.25, and glycerol a t 2.25 is superior to glycerol at 3; i. e., the best sorbitol and glycerol resins have the same ratio of acid to reacting hydroxyl-namely, 0.75. I n Table V the comparative performances Esr ADHESION FLOW TACK PRINT FREE of the resins are summarized. Relative performance is judged to be equal (shown by dots) if the performance ratings differ by only one step, and better (plus) or worse (minus) if more than one step. I n tabulating the comparisons, the two air-dried samples, with and without drier, and the five baked samples SORBITOL 3 -VS. GLYCEROL 3 tamzzza were arranged in two groups as shown. The best sorbitol resin (S-3) is superior to FIGURE1. COMPARATIVE BEHAVIOR OF SORBITOL 3 AND GLYCEROL 3
1226
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 30, NO. 11
on cold check. The latter test consisted of alternating 4-hour cycles a t 140" and 35" F. The glycerol resin, in this top coat test, rated slightly higher in toughness.
Analysis of Resins for Polyhydric Residue As a direct chemical proof of anhydro formation during esterification, the sorbitol ester gums and air-drying alkyds were taken apart, and the polyhydric residue was examined for identity with the starting material. Saponification of the alkyds took place readily in cold alcoholic potash-benzene solution, but the ester gums proved more resistant and required refluxing for several hours or standing in the cold for several days. The water-soluble polyliydroxylic residues thus set free were separated from the organic acids by suitable solvent extraction methods and were recovered as thick brownish sirups. For identification use was made of the m-nitrobenzal method of Bleyer, Diemair, and Lix (I),which yields sorbitol as the tri-m-nitrobenzal, melting a t 168" C., when an excess of the aldehyde is employed. However, the crystalline m-nitrobenzal derivatives, obtained from a series of sorbitol alkyds, from an ester gum made a t 250" C., and from fatty-acid-modified alkyds, had the FIGURE2. COMPARATIVE BEHAVIOR OF SORBITOL 3 AND SORBITOL 2.25 same melting point and mixed melting point of 194" C. Analysis showed the compound to the corresponding best glycerol resin (G-2.25) in hardness, be a di-m-nitrobenzal of a monoanhydrosorbitol, C6HsO(OH)4. The same monoanhydrosorbitol or sorbitan was identified rubbing, drying time (tack-free and print-free), and hydrocarbon and grease resistance, but is inferior in color, luster, as the di-rn-nitrobenzal in a monoanhydrosorbitol fraction humidity, and salt spray resistance. But resins S-3 and G-2.25 boiling between 225" and 250" C. a t 3 mm., made by the action of phosphoric or sulfuric acid on sorbitol a t 145" C. are superior to G-3 in weather, humidity, and salt spray resistance, although 'resin G-3, made a t the stoichiometric ratio, should have less free hydroxyl than the others. The controlling factor for moisture resistance appears to be reaction time rather than stoichiometric ratio, since resins S-3 and G-2.25 were reacted much longer than G-3. Also, resin 8-2.25 should have more free hydroxyl than 5-3, according to Kienle's view. Hence it should be more hydrophile and less hydrophobe, and accordingly have inferior SALT SPRAY 1 WEATHER moisture resistance and superior hydrocarbon resistance. Actually resin S-3 is superior in hydrocarbon resistance, and there is virtually no difference, except for salt spray, in moisture resistance. II I1 II U I n a lacquer enamel test the order of merit 1) LUSTER /I RUBBING /I HARDNESS was quite different (G-3 > G-2.25 > 5-2.25 > S-3), as shown in Table VI. The formulation used was that of a standard nitrocellulose lacquer enamel, tests being made on airdried samples and on samples baked 1 hour 11 TACK 1) PRINTFREE LOW at 200" C. The regular commercial resin used proved slightly inferior to 5-2.25. Actual performance is given for the standard commercial resin. No differences between the three were found when tested in a wood sealer, although all three were slightly less tough than the regular comSORBITOL 3 VS. GLYCEROL 2.25 mercial resin. When tested in a topcoat wood lacquer, the BEHAVIOR OF SORBITOL 3 AND GLYCEROL 2.25 FIGURE3. COMPARATIVE 5-3 resin was the only one to have an A rating
I
-
NOVEMBER, 1938
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLEv.
1227
- --
SORBITOL .4ND GLYCEROL AIR-DRYINGALKYDS IN SYNTHETIC ENAMELS S-3 V S . G-3 0---G-2.25 US. G-3----S-3 VS. S-2.25 7--5-3 U S . G-2.25---Air-dried--Baked-Air-dried7 Baked r h i r - d r i e d - --Baked--Air-dried--Baked-S-3 G-3 S-3 G-3 G-2.25 G-3 G-2.25 G-3 S-3 S-2.25 9-3 5-2 2 5 5-3 G-2.25 5-3 G-2 25
Gasoline resistance Oil resistance Grease resistance Alcohol resistance Weather resistance Humidity resistance Salt spray Uviarc Color Luster Rubbing Hardness Tack Print-free Adhesion Flow
.. .. .. .. .. ..
+. . . - . ++
..
..
. . . . . . . .
..
. . ..
.. ..
++ ..
..
+
+
-
. . . . . . . .
TABLE VI.
-
.
. . . .
- + - + + '. .1 .+ . . . ..
-
-
.
. . . .
-
+
-
+ . .
.
-- +++- +-
.
+-
, .
-
. .
+ . . ..
+ . . . . . . . . . . . . . . . . . . . .
+
.
. . . . ..
.
.
.
.
. .
. .
. .
. .
. .
..
. . . .
.
.
.
.
.
.
. .
.
. .
.
. .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.- . .. .. .. ..
..
- + :++ . . . . . . .
. . . .
.
.
.
.
.
.. + .. .. . . . . . . .
.
.
.
.
.
. . . . + . . . . . . . .
. . . .
-
.. -
+
..
+-
-- ++ -- + +- .. . . . .
+ +
+-
.. ..
. . . . . .
-
.. -
+..
+
-
.. + . . . . . .
NITROCELLULOSE LACQUER ENAMELS
+. . . - .
+- +- + . . . .
+. .
++ ++ -
. . . . . . . .
-
--S-2.25 vs. G-3----S-3 us. S-2.25----G-2.25 us. G-3-Air-dried-Baked-Air-driedBaked-Air-dried-BakedS-2.25 G-3 3-2.26 G-3 5-3 S-2.25 s-3 s - 2 . 2 5 G-2.25 G-3 G-2.25 G-3
Gas resistance Oil resistance Grease resistance Alcohol resistance Humidity resistance Salt spray Uviarc Color Luster Rubbing Hardness Tack Print-free Adhesion Flow
+-+-
..
..
-
. . . . . . . . . . . . . . . .
. . . . . . .. - ' + -
++ ++ +++ ++ +
-
. . . . . .
, .
-
..
.
+
-
++ +
-
.
-
+ + . .
-
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This fraction was used in preparing the sorbitan ester gum described in Table VII. The polyhydric saponification residue from this sorbitan ester gum yielded the same sorbitan, di-m-nitrobenzal, melting a t 194' C. I n no case could sorbitol be found, using the m-nitrobenzal method, in a resin made above 145" C. Control experiments showed that no internal anhydridization or etherification of sorbitol took place during saponification and recovery of the polyhydroxylic residue. By way of comparison, the only identifiable mater-soluble product obtained on saponifying corresponding glycerol resins was the original glycerol. There are fifteen theoretically possible tetrahydric monoanhydro products of sorbitol. The identification of the one isolated as the di-m-nitrobenzal is being studied. It is evident, then, that resinous esters made from hexitols a t elevated temperatures are not derivatives of a 6-reactive compound, but primarily of 4-reactive monoanhydrohexitols or hexitol inner ethers. Whether inner etherification precedes esterification, or whether a resinous hexitol ester undergoes intramolecular loss of water to form esters of inner ethers, is not yet known. Probably both types of reaction take place. I n rosin ester gum, where the rosin does not begin to react until 240-250" C. is reached, there is ample time for thermal decomposition of the hexitol. I n alkyds, however, the primary esterification of phthalic anhydride proceeds a t temperatures below 176" C. so that in this case sorbitol or manni%olphthalate may be the intermediates. In this connection Brigl and Gruner (8) showed that mannitol diesters can lose mater readily when heated with certain acidic catalysts, to form mono- and dianhydro products. There is still an apparent discrepancy between the 4 hydroxgls shown to be available and the optimum of about 3 acid equivalents established by experiment. This could be explained by assuming that two tetrahydroxy monoanhydrohexitola were formed in equal amounts, and that one of these then lost a second molecule of water to form a dihydroxydianhydrohexitol. This mould now leave three available
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hydroxyls. At least one dianhydrosorbitol is known (7), but the rosin ester gum produced from it is much softer than that from sorbitol or sorbitan, as Table VI1 shows.
TABLE VII.
ESTERGUMSFROM SORBITOL, MONOANHYDRODIANHYDROSORBITOL
SORBITOL, AND
Hours
Alcohol Sorbitol Monoanhydrosorbitol Dianhydrosorbitol
Rosin at % Equiva- 300" lents C. Yield 3 72 2.76 3 68 3.0 8 84 3.1
-4cid
No. 19 14 28
Softening Pooint, Color C. 40 112 30 108 60 80
Therefore a dianhydrorosin ester could hardly constitute half of the finished resin. It appears, then, that the behavior of the hexahydric alcohols in the technically important resins cannot be predicted from the behavior of the lower members of the straight-chain polyhydric alcohol series.
Literature Cited (1) Bleyer, Diemair, and Lix, 2. Untersuch. Lebensm., 65, 37 (1933). (2) Brigl and Griiner, Ber., 66B, 1945-9; 6713, 1582-9 (1934). (3) Callahan (to E. I. du Pont de Nemours & Co., Inc.), U. S. Patent 2,003,068 (May 28, 1935). Hopkins and McDermott (to E. I. du Pont de Nemours & Co., Inc.), Ibid., 1,974,742 (Sept. 25, 1934). (4) Freudenberg and Rogers, J . Am. Chem. Soc., 59, 1602-5 (1937); Muller, Arb. Ungarischen Biol. Forsch.-instit., 8 , 405 (1936). (5) Hovey, A. G., paper presented as part of Symposium on Organic Plastics before Div. of Paint and Varnish Chemistry at 93rd Meeting of A. C. S., Chapel Hill, N. C., April 12 to 15, 1937. (6) Kienle, R. H., JXD. ENG.CHEM.,22, 593 (1930). (7) Muller and Hoffman (to I. G. Farbenind. A.-G.), U. S. Patent 1,757,468 (May 6, 1930). RECEIVED September 23, 1937. Presented before the Division of Paint and Varnish Chemistry at the 94th Meeting of the d m e r ~ c a nChemical Society, Rochester, N. Y., September 6 t o 10, 1937.
