Mineral Oil Deterioration A Revised Grignard Apparatus A. G. ASSAF
AND
E. K. GLADDING, iMassachusetts Institute of Technology
T
end of which is tapered and ground, and which fits into a groundglass aperture with re-enforced walls. The other end is sealed by means of about 4 cm. of pressure tubing (whose inner walls were previously wet with castor oil) which is wired to the tube and rod, a type of seal which gave no leakage trouble. The Grignard reagent can thus be easily transferred from reservoir C to buret F by manipulation of this joint. E is a greaseless stopcock similar to D except that the glass rod is 8 mm. in diameter. The 2-cc. reagent buret, F , graduated to 0.02 cc., was calibrated while the rod was in it. Reservoir C, joint D, and the top of buret F are covered with black cloth to protect the reagent from light. The reaction Rask, G, has a volume of about 70 cc., is stirred by the method previously described (C), and simply slides on and off of the male joint, H . The gas buret, J , is a 25-cc. buret graduated to 0.05 cc. In order to take care of the gas expansion upon heating, a reservoir was provided at the bottom of the buret. The purifying train consists of a heated tube containing copper gauze, followed by tubes of Dehydrite, phosphorus pentoxide, and Ascarite as previously described (4).
HE continued uRe of a Grignard reagent (methyl magnesium iodide) in the study of mineral oil deterioration has led to the refinement of the apparatus. In conjunction with the revision of the apparatus, various tests have been carried out to obtain quantitative determinations with the Grignard reagent of ketones, esters, and peroxides such as may be found in petroleum oils. For the past few years the Grignard apparatus as described by Larsen ( 2 , 4 ) has been used in these laboratories as an analytical tool in the study of mineral oil deterioration. The results obtained were very promising, and have justified the improvement of the apparatus and procedure so as to give more consistent and accurate results, and to increase the speed and ease of manipulation. Apparatus
Procedure
The following description explains Figure 1. The Grignard reagent (methyl magnesium iodide) is introduced through the female joint and stopcock at the top of reservoir C (capacity 500 cc.). One filling is enough for at least 300 determinations. The greaseless stopcock, D , consists of a glass rod (5 mm.), one
Flask G is cleaned after use by washing with successive portions of benzene, acetone, dilute hydrochloric acid, distilled water, and methanol. Ether was not used as a final solvent because it was found that slight traces of ether vapor rapidly dissolve in the isoamyl ether of the Grignard reagent, creating a reduced pressure. The flask is dried by gentle heating with a Bunsen flame while blowing in a slow current of dry nitrogen by means of a glass tube which rojects to the bottom of the flask. After the $ask is dry, the flame is withdrawn, and nitrogen is allowed to flush the flask for about 15 minutes. All apparatus, such as reaction flasks and pipets, are kept in a hot-air oven when not in use. To save-time, it is advisable to have two reaction flasks. The oil buret, I , and male joint, H , are cleaned similarly by placing rubber tubing at the mouth of the buret and drawing up through Joint H successive portions of the same cleaning solvents used above. Stopcock iM is then opened, and a Bunsen flame is gently waved over joint H and buret I as nitrogen is sweeping out through them. Nitrogen is allowed to flush through for about 15 minutes. Joint H is now greased and the dry flask, G, attached to it. This joint is a dripjoint and extends far enough downinto the female part so that there is no chance of the reagent’s touching the grease. The stopcock a t the base of buret I is then closed, and stopcock K at the top of the gas buret is adjusted so that nitrogen flows through the groove in the stopcock and out into the atmosphere. Nitrogen is al-. lowed to pass through for 5 minutes, after which stopcock K is adjusted so that the buret is connected to the system, and stopcock M is closed. The system is tested for leaks by lowering the leveling bulb and observing whether the reading remains constant for at least 5 minutes. A beaker of water whose temperature is determined to a tenth of a degree is brought up under flask G, and after 5 minutes the reading on buret J is taken. Stopcock L is opened and then closed to allow a few cubic centimeters of nitrogen to flow into the reservoir, and leveling bulb N is lowered slightly so as to create a reduced pressure. The reading on buret F is taken, and stopcock E is opened slightly to allow 1 cc. of reagent to drip into reaction flask G . Five minutes are allowed for the system to come to equilibrium, after which a reading is taken on buret J. The initial displacement is always larger than the volume of reagent added. This so-called blank reading is
FIGURE 1. GRIGNARD APPARATUS 164
ANALYTICAL EDITION
MARCH 15, 1939
not always constant, and ranges from 0.20 to 0.80 cc., depending on how dry the system is. A suitable and weighed amount (4to 8 cc.) of oil is now transferred from the weighing vessel to buret I (in small portions, since I holds only 4 cc.). The oil is introduced slowly into reaction flask G so that no appreciable afterdrainage results. The solenoid stirrer is started, and thereafter the procedure is the same as that previously described (e) except that 4 cc. of aniline are added instead of water, and the temperature of the water surrounding flask G is taken t o a tenth of a degree upon each reading of the gas buret. After the volume readings of methane evolved at room temperature have been obtained, a temperature correction is applied by the use of the following formula which also brings the volumes of methane evolved to normal temperature and pressure conditions:
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However, it was desirable to test the sensitivity of the Grignard reagent with the esters of high molecular weight such as may be formed in oils. Therefore “ester gum,” preponderantly a triglyceryl ester of, abietic acid (formula CeaHezOs), was dissolved in standardized xylene and treated with methyl magnesium iodide. The amount of free abietic acid in the sample was obtained by potentiometric titration. The results obtained are listed below: Moles of CHsMgI per Mole of Ester Evolved Added Consumed
Run 1 2 3 4
Av.
where P = atmospheric pressure T B = gas buret temperature Vz = final reading on gas buret VI = initial reading on gas buret Ve = approximate volume of system Tel = initial temperature of water surrounding reaction flask Tc2 = final temperature of water surrounding reaction flask The results obtained are expressed as cubic centimeters of methane (at normal temperature and pressure) evolved per kilogram of oil, but may be transferred into other equivalents such as cubic centimeters of oxygen per kilogram. Aniline was substituted for water in the standardization of the Grignard reagent after investigation of the error caused by the high vapor pressure of water a t room temperature. Standardization with water (using a drying tube as described by Larsen, 4) gave a value of 13.5 cc. of methane evolved per cubic centimeter of Grignard reagent, while with aniline the value obtained was 9.2 cc. Experiments made by adding water to the clean and dry system showed that errors of this order of magnitude were caused by the vapor pressure of water, and not by incomplete reaction with aniline. Check standardizations yielded 9.40, 9.10, and 9.16 cc., the maximum deviation from the mean being less than 2 per cent.
Results OXYGEX. It is well established that oxygen reacts with Grignard reagents: 2 CHaMgI
+ 02 +2 CHaOMgI
Experiments with gaseous oxygen and methyl magnesium iodide indicate that the reaction is rapid and complete. I n oxidized oils, therefore, the Grignard reagent reacts not only with the oxygenated compounds but also with dissolved oxygen. The data on the measurement of dissolved oxygen in oils by the Grignard reagent are not yet complete, but the higher Grignard (‘added” values (1) of oils saturated with oxygen as compared to those saturated with pure nitrogen indicate that the reagent and the dissolved gas do react. KETONES.Quantitative measurements of benzophenone by the Grignard reagent have been made by Kohler and his co-workers (3). I n order to test the accuracy of the apparatus, a solution of known concentration of benzophenone in xylene (distilled over sodium wire) was treated with the Grignard reagent. The results obtained (1.04 moles of methyl magnesium iodide consumed per mole of benzophenone) attest to the effectiveness of the apparatus. ESTERS. A known solution of phenyl benzoate in dry xylene, upon which a blank test had been made, was prepared and treated with the Grignard reagent. The results obtained (1.92 moles of methyl magnesium iodide consumed per mole of phenyl benzoate, with no methane evolved) gave good evidence of the sensitivity and accuracy of the methyl magnesium iodide with esters of this type.
3.5 4.0 3.5 4.0 3.7
5.8
2.3 1.8 2.8 2.7 2.4
5.8
6.3 6.7 6.1
The theoretical amount of Grignard consumed is 6.0 moles. Whether the methane evolved is due to splitting of the ester and subsequent enolization to give an active hydrogen is open to conjecture. At any rate, the significant fact is that the “Grignard consumed” value gives a measure of the ester content (3). However, more determinations with such high molecular weight esters (and in a purer state) must be made before any definite conclusions are drawn. PEROXIDES. During the study of the oxidation of decalin, a crystalline peroxide was formed. The decalin was heated in an air-oven a t 90” to 100” C. while oxygen was bubbled in through a sintered-glass disk for approximately 46 hours. The decalin wag then vacuum-distilled until a strawcolored, rather viscous liquid remained which, upon cooling, gave a mush of needlelike crystals. Upon filtration and recrystallization from ligroin, long white needles of a melting point 94-5” C. were obtained. Assuming the peroxide to be 1molecule of decalin plus 1molecule of oxygen (CI~H180J, its theoretical percentage composition is 70.5 per cent carbon and 10.62 per cent hydrogen. A carbon-hydrogen analysis substantiated this assumption, values of 69.8 per cent carbon and 10.4 per cent hydrogen being obtained. A weighed amount of the peroxide was then dissolved in anhydrous xylene and treated with the Grignard reagent. Methane was evolved, indicating an active hydrogen. Since the structure of decalin peroxide is more or less in dispute, it seemed natural to postulate that this peroxide is of the R--0-0-H type. Assuming this to be true, one mole of peroxide would react with 2 moles of methyl magnesium iodide (one of them evolving methane). A comparison of the theoretical vs. experimental values based upon this assumption was favorable: 1. 0.96 mole of CHaMgI evolved per mole of decalin peroxide 2. 1.07 moles of CHaMgIadded per mole of decalin peroxide
The Grignard reagent apparently reacts quantitatively with this type of peroxide. TABLE I. SUMMARY OF RESULTS Compound Benzophenone Phenyl benzoate “Ester gum” Decalin peroxide
Moles of CHaMgI per Mole of Compound Evolved Added Consumed Theoretioal(1) 1.04 1.04 1.00 None None 1.92 1.92 2.00 3.7 0.96
2.4 1.07
6.1 2.03
6.0 2.00
Summary
A compilation of the results obtained, given in Table I, shows the accuracy of the quantitative determination, by the Grignard reagent, of the types of compounds-ketones, esters, and peroxides-which one may expect to find in oxidized petroleum oils.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Acknowledgment The development of the application of the Grignard reagent to mineral oil deterioration is part of a joint research project of the Massachusetts Institute of Technology and the ,Utilities Co-ordinated Research, Inc. (Association of Edison Illuminating Companies), on electrical and chemical studies of insulating oil deterioration. The authors wish to acknowledge the cooperation of the Committee on Insulating Oils and Cable Saturants, U. C. R., Inc., Herman Halperin, chairman, and other committees representing the oil-refining and electrical manufacturing companies.
VOL. 11, NO. 3
The authors also wish to express their indebtedness and appreciation to J. C. Balsbaugh and J. L. Oncley for their interest and cooperation.
Literature Cited (1) Balsbaugh and Oncley, IND. ENG.CHEM.,31, 315 (1939). (2) Balsbaugh, Larsen, and Oncley, Annual Report to Utilities Coordinated Research, Ino. (Sept. 1,1937). (3) Kohler, Stone, and Fuson, J. Am. Chem. Soc., 49, 3180-7 (1927). (4) Larsen, R. G., IND. ENG.CHEM.,Anal. Ed., IO, 195 (1938). RECEIYED October 6,1938.
Improved Gas Analysis Apparatus Employing a Simplified Automatic Absorption Pipet C. M. BLAIR AND J. H. PURSE Carbide and Carbon Chemicals Corporation, South Charleston, W. Va.
I
N T H E past few years attention has been directed toward
the design of gas-absorption pipets by which the rate of absorption of gases in liquid reagents may be increased. Egerton and Pidgeon (2) described a device whereby the absorbing reagent was sprayed through the gas in the form of a fountain. This was effected by forcing the reagent through a constriction in the pipet by manually raising and lowering a reservoir of mercury connected to the pipet. An improved modification was devised by Egerton and Smith (3) but the fountain was still effected by manual operation. Later, Weydanz (7) published a description of a pipet in which a portion of reagent was trapped in a specially designed cup as the sample was introduced into the pipet. This liquid then dripped through the gas from capillary holes in the cup. The glass blowing of the pipet was involved and little saving in time was gained. The first automatic pipets were developed and in some forms patented by Huff (4). I n these forms a continually fresh surface of absorbent in contact with the gas was secured by the motion, inside the pipet, of a glass-covered iron piston actuated by an outside electromagnet. Later another mechanized gas analysis apparatus was devised by Kleiber (5) and modified by Winchester (8, 9). The complexity of this apparatus precludes its general use in gas analysis. I n the Huff electromagnetic pipets the rate of agitation is determined by the time required for the piston to fall (or rise) by gravity through the reagent. Consequently, a single standard pipet will not give optimum results with all reagents, and it is necessary to have pipets of slightly different design for the use of reagents of markedly different viscosities and specific gravities. The loose piston makes it necessary to exercise extreme care in changing solutions and in cleaning the pipets to avoid breakage. These difficulties are overcome by a pipet that is designed in the same general manner as the Huff pipet and utilizes alternating air pressure as the pumping mechanism in a way which is analogous to that described by Huff in his original patent application dated July 22, 1931. This design was not patented by Huff and does not appear to have been published elsewhere.
Apparatus The details and dimensions of the pipet are given in Figure 1. The pipet occupies approximately the same space and can be
OPENINGS PULLED OUT NOT DRILLED
P L A N OF P I P E T
lOMM.Nl
AND ELEVATION OF PIPET FIGURE 1. PLAN
