OIL SPRAYS Chemical Properties of Petroleum Oil Unsaturates Causing Injury to Foliage Experimental evidence indicates that the unsaturated hydrocarbons of the lubricating fractions of petroleum oils are not toxic to foliage until they are oxidized to asphaltogenic acids. At ordinary temperatures this oxidation takes place to a measurable degree only in the presence of air and light. Using apricot leaves as a testing medium, it was found that the toxic threshold is reached when approximately 0.5 per cent of asphaltogenic acids are formed. The relation of viscosity and percentage of unsaturates present in a spray oil to its susceptibility to oxidation in light of various intensities is discussed.
R. P. TUCKER California State Department of Agriculture, Sacramento, Calif.
W
HEN petroleum spray oils came into prominence some years ago Gray and de On&(1) showed that the relative toxicity of the various oils to foliage was roughly proportional to the amount of unsaturates present in the oils. (In the present discussion the unsaturates are considered as making up that portion of a petroleum oil which is removed by 37 N sulfuric acid when the oil and acid are mixed in the manner prescribed in the unsulfonated residue tests of the California State Department of Agriculture; i. e., an oil having an unsulfonated residue of 90 is considered as containing 10 per cent of unsaturates .) By means of the unsulfonated residue test, the petroleum oils used as insecticides are separated roughly into two classes, conveniently designated as “summer or foliage” oils, and “winter or dormant” oils. It is quite generally accepted that injury to foliage is much less apt to occur when the unsaturates are completely removed from an oil than when appreciable amounts remain. Unfortunately a high degree of refinement increases the cost of a spray oil. Largely because of this fact, a considerable difference of opinion has arisen as to the maximum amount of unsaturates which can be safely tolerated in the foliage class of oils; the amount ranges from 15 down to 5 per cent. From a regulatory standpoint it would be desirable to have more accurate specifications for the percentages of unsaturates allowable in the foliage spray oils. Consequently the writer made a study of the problem, why are the unsaturates of petroleum oils toxic to foliage? This paper presents a resume of the results obtained.
An oil was considered toxic when it caused the portion of the leaf upon which it had been applied to turn yellow. In many cases the injury spread rapidly to the entire leaf and it usually dropped off. I n other cases the injured portion of the leaf turned black and dropped out, leaving the rest of the leaf apparently as healthy as before treatment. This toxic condition is designated by the term “burning.”
Penetration of Apricot Leaves by Petroleum Oils Petroleum oils penetrate the upper surface of apricot leaves very slowly, probably because of the small number of stomata located on this surface of the leaf. The under side of an apricot leaf contains a great many stomata. The petroleum oils penetrated this surface of the leaves rapidly during the daylight interval, with no appreciable difference in the rate of absorption when leaves in full sunshine were compared to leaves in the shady portion of the tree. As darkness came on, a sharp decrease of penetration was noted, and this condition continued until daylight. When petroleum oils containing from 25 to 50 per cent unsaturates were placed on the upper surface of apricot leaves, no toxic effects were noted in a 2-month interval. When the same oils were smeared on the under side of the leaves, they began to turn yellow in 4 to 7 days and soon developed the severe toxic conditions already described. The results of these tests indicated that petroleum oils enter the leaf through the stomata while these organs are open under the influence of light. The great difference in the
Methods of Oil Application to Foliage Where the study involved the application of the various oils to foliage, the methods of procedure were simplified in order to keep interfering reactions down to a minimum. I n most of the experiments the samples of pure oil were smeared on individual leaves. This procedure allowed selection of healthy leaves and daily investigation of results. Apricot leaves were used in most of the field tests as an example of a foliage which is not too resistant to the action of the oils and whose general leaf characteristcs, such as shape, texture, etc., allow a study of the more obvious phases of oil penetration. 458
APRIL, 1936
INDUSTRIAL ANI) ENGINEERING CHEMISTRZ:
toxicity noted when dormant oils were smeared on the upper and lower surfaces of the leaves indicates that the area of disturbance of these oils lies within the leaf rather than on the surface.
Effect of Light on Toxicity of Petroleum Oils In a series of preliminary observations on the effect of various petroleum oils on apricot leaves, the following results were noted: 1. When medicinal mineral petrolatum or other waterwhite oils, with viscosities greater than kerosene and containing no appreciable amounb of unsaturates, were smeared on the under side of apricot leaves, no yellowing or blackening of leaf tissue was noted over long periods. I n fact, some leaves oiled early in the season remained green until autumn, although large amounts of oil were present in the interior of the leaves. 2 . When petroleum oils containing 25 per cent or more of unsaturates and with viscosities from 65 to 400 Saybolt seconds were smeared on the under side of apricot leaves, no ill effects were noted for 2 or 3 days. From the fourth to the seventh day the oiled areas began to turn yellow. The toxic condition then progressed at different speeds, depending upon the oils used. 3. When the same dormant oils were smeared on the under side of apricot leaves and Manila paper bags were tied over the twigs as soon as oil absorption was noted, no indication of burning was apparent when the bags were removed at the end of 15-18 days. If the twigs were then removed from the tree, placed in water, and kept in dim light, no further evidence of burning was found for the 10 to 15 days elapsing before the leaves withered. The oiled leaves left on the tree blackened a few days after removal of the bags. When the twigs were bagged for more than 3 weeks all the leaves within the bags, whether treated or untreated, began to turn yelloaso that longer testing periods were not practicable. In further tests on the inhibiting effects of darkness on the toxic properties of the dormant oils to foliage, it was found that light of intensities below 5 foot candles or lumens per square foot, as registered by a Westinghouse foot candle meter, gave the same results as were obtained by the use of paper bags. Beginning with 25 lumens, injury was noticeable, but 100 lumens apparently gave as rapid injury as exposure to direct sunshine. The comparative values of these light intensities may be judged by the following rough standards (in lumens) : 0.2 5.0 25.0
100.0
Print barely discernible Room well lighted with artificial light Under dense shrubbery on north side of building; sun shining Deep shade of s h e with sun shining
The results of these preliminary experiments indicate that the difference in toxicity to foliage of petroleum oils with the unsaturates both removed and present, is due to the relative resistance of the two types of oils to chemical change induced by light. That this chemical change in the dormant type of oils was one of oxidation was definitely indicated by exposing dormant type oils to sunlight with free exposure to air and to sunlight with air excluded. In every case where exposure to sunlight and air had lasted long enough, the oils b 1a c k e n e d o r yellowed apricot foliage in subsequent darkness as readily as in light; the oils exposed to sunlight, but out of contact with air, were no more toxic in darkness than the original oils when applied under similar conditions.
459
Toxicity of Asphaltogenic Acids The oxidation products of petroleum oils exposed to air at temperatures below 150' C. were shown by Staeger ( 5 ) , Haslam (Z),and others to be a complicated series of compounds with acidic properties. A small portion is watersoluble and rather simple in structure. The greater percentage, classed as the asphaltogenic acids is oil-soluble during the first stages of oxidation but forms an insoluble sludge as oxidation progresses. The oil-soluble asphaltogenic acids can be separated from the accompanying unoxidized oil by shaking with 50 per cent alcohol and sodium hydroxide, and can be quant,itatively determined by the following method, used for extracting ordinary soap acids from a mixture of these acids with a petroleum oil: Twenty-five grams of oil are weighed in a pear-shaped separatory funnel. Then 100 cc. of petroleum ether are added, and the mixture is shaken with 50 cc. of 50 per cent alcohol made alkaline with a little sodium hydroxide. After sett,ling, the alcoholic layer is drawn off, the alcohol evaporated, and the water solution of soaps acidified with hydrochloric acid. The acids are then extracted with ethyl ether and collected in a tared beaker. The relation between the amount of asphaltogenic acids present in an oil and the toxicity of the oil to foliage was studied as carefully as circumstances permitted. Owing to the small quantities of oil absorbed by the leaves, it appeared impossible to recover the toxic oil from the injured areas in sufficient amount and purity for chemical examination of the changes which had taken place in the oil in order to make it injurious to the leaves. As a substitute for this ideal method the following procedures were employed: METHOD1. Samples of foliage and dormant spray oils derived from naphthene- and paraffin-base crudes were exposed to sunlight and air for periods varying from 7 to 30 days. This aging interval is roughly comparable to the time required for visible damage t o occur when leaves coated with dormant oils are exposed to sunlight and air. The rapidity with which asphaltogenic acids are formed in a petroleum oil when the oil is exposed to light and air depends to a large extent upon the surface in contact with the air. In order to obtain sufficient oxidation ithe relatively short intervals desired, a number of expedir were used t o increase the area of oil exposed; the soaking of g wool with the oils and the use of large crystallizing dishe containers proved most satisfactory. In all cases the di containing the oils, usually in 30-50 gram lots, were placed of doors so that they received direct sunlight for 2 t804 hov day. A t the end of the aging periods, the percentages of the asph genic acids in the various oils were determined. Samples 01 untreated oils, of the oils after aging, and, in some cases, of aged oils with the asphaltogenic acids removed were smc on the under side of apricot leaves. Bags were tied over the twigs as soon as oil absorption was noted and allowed to remain for 10 to 18 days. At the end of this time the bags were removed and the relative damage to the leaves caused by the original oil and the same oil after aging was noted. Although the results showed some irregularity, it appeared that when oxidation had progressed far enough to produce 0.5 per cent of asphaltogenic acids, the oils injured the leaves in darkness. No disturbance was noted when the amount of acids was less than 0.4 per cent. With 1.0 per cent acids present, the injury was unmistakable; 2.0 per cent blackened or yellowed the foliage in 2 or 3 days. With the asphaltogenic acids removed, either no injury or, at most, only slight injury was noted. Results of a number of the tests are given in Table I. METHOD2. The acids were extracted from oxidized samples of oils, and various percentages of the acids were dissolved in oils of the mineral petrolatum type. These water-white oils were inert towards foliage. When 0.7 to 1.5 per cent of the acids were dissolved in them, the combination proved very toxic to leaves which were bagged, as well as to leaves in light. No difference was noted in the relative toxicity of the various samples of asphaltogenic acids used, regardless of whether t.he acids had been obtained from dormant oils aged in sunlight and air, or whether they had been removed from mineral petrolatum type oils oxidized bv heating in a drying oven at 100" C. for a number of davs.
.. I
460
INDUSTRIAL AND ENGINEERING CHEiMISTRY
Effect of Unsaturate Percentage on Formation of Asphaltogenic Acids
VOL. 28, NO. 4
TABLEI. RELATIOX OF ASPHALTOGENIC ACIDSIN A SPRAY OIL AND ITS TOXICITY TO APRICOT FOLIAGE
Table I shows that oil 5 has a viscosity of Burn on Apricot Leaves 77 Saybolt seconds and an unsulfonated residue Saybolt UnsulAsphal- with Twigs Oil Viscosity fonated togenio of 91 per cent (unsaturates, 9 per cent) which Bagged NO. at 100' F. Residue Treatment of Oil 10-18 Days Acids place it in the present foliage class of oils. When Sec. Per cent P e r cent aged in sunlight for 8 to 13 days, approximately 1 138 Original oil 65 0.54 Slight No. 1 aged 13 days in sunlight as high percentages of asphaltogenic acids were 1-A 1.68 Bad formed as with oils of 50 to 60 per cent unsul2 101 Original oil 65 0.44 None 2-A 0.87 Slight No. 2 aged 7 days in sunlight fonated residue and much greater viscosities. 2-B 0.09 No. 2-A with acids removed None 2-c Bad No. 2 aged 7 days in sunlight 1.61 This result was checked a n u m b e r of times 2-0 Slight No. 2-C with acids removed Nil with other oils of the so-called foliage type and 2-E No. 2 aged 13 days in sunlight Bad 0.91 was quite uniformly obtained. If more than 3 3 Paraffin-base motor oil 420 50 0.05 None No. 3 aged 12 days in sunlight to 4 per cent unsaturates were present in an oil, 3-A 0.26 None 3-B No. 3 aged 8 days in sunliqht 0.65 None sufficient asphaltogenic acids were produced in 3-c No. 3 aged 10 days in sunlight 0.98 Slight 3-0 2.32 No. 3 aged 29 days in sunlight Bad 7 to 30 days in the artificial aging tests carried 3-E No. 3 - 0 with acids removed Nil None out in dishes to cause injury to foliage. When 3-F No. 3-C with acids removed Nil None the same oils were smeared on apricot leaves, a 4 420 60 Naphthene-base motor oil 0.10 None 4-A 0.65 No. 4 aged 8 days in sunlight Medium difference was noticeable between their action 4-B Nil No. 4-A with acids removed Slight and those with unsulfonated residues below 75 Original oil (foliage type) 77 91 0.01 None per cent. That is, no toxic effects to the leaves 5-A No. 5 aged 30 days in sunlight 0.92 Bad No. 5-A with acids removed Nil 5-B None were noted with oils containing 5 to 10 per cent No. 5 aged 13 days in sunlight 5-C 1.55 Bad of unsaturates, whereas the oils with large per6 140 100' Mineral petrolatum Nil None centages of unsaturates were invariably toxic. 6-A No. 6 after 10 da e on hot late 6.15 Bad 6-B sods remove$ No. 6-A with Nil Very It was apparent that the aging tests, as carried slight No. 6 aged 14 days in sunlight 6-C 0.17 None out. Dresented a more favorable omortunitv for oxidakon of oils with unsaturates between 5 and 10 per cent than occurs in the interior of leaves. In further tests it was assumed that visible light of all was noted. As mentioned, 1 per cent of asphaltogenic acids dissolved in the same inert oils invariably burned foliage even intensities makes the unsaturates sensitive to oxidation, but in darkness. that the low intensities prevailing in the interior of leaves One to two per cent of linolenic acid dissolved in inert oils and the large amount of water present slow down the formation of asphaltogenic acids and make their production roughly was somewhat toxic to apricot leaves but not to the extent proportional to the percentage of unsaturates present in the shown b y the petroleum acids. The question, why are the asphaltogenic acids toxic to oils. foliage and the hydrocarbons from whence they are derived While this supposition was not definitely proved, the results apparently not, presents an interesting problem. of several experiments similiar to the following indicate that The interfacial tension between the acids and material it is a possible explanation of why foliage oils containing wreciable amounts of unsaturates have been used successsaturated with water is much less than that between the same ,', as far as their toxic action on foliage is concerned. material and unoxidized petroleum oil. It is probable that four oils chosen had the following properties: the acids can pass through the walls of the leaf cells more freely than can the unoxidized oils but not more freely than Saybolt Unsulfonated Asphaltogenic oleic or stearic acids. Further, the studies of Knight (S), Oil Viscosity Residue Acids Young ( 6 ) , Rohrbaugh (4), and others indicate that even Sec. P e r cent P e r cent inert oils of the mineral petrolatum type pass through the A 102 96 Nil B 106 74 0.17 walls of leaf cells. It does not seem, therefore, that the toxicity 60 104 89 0.10 DO 104 92 0.10 of the asphaltogenic acids is due primarily to their acid charcI and D were blends of A and B. acter but rather to their further breakdown into colloidal asphaltic compounds; during this reaction they may absorb Twenty-five grams of each oil were poured with 200 cc. of oxygen from the cells which they surround or to which they water into 2-liter Erlenmeyer flasks. The flasks were wrapped have gained entrance. in green paper and placed where the sun shown upon them approximately 4 hours a day. At the end of 30 days the asConclusions phaltogenic acids were determined with the following results : The data indicate that the hydrocarbons of petroleum oils A, 0.01 per cent; B, 0.76; C, 0.45; D , 0.45. are not toxic to foliage in a chemical sense until they are If 0.50 per cent asphaltogenic acids represents the threshoxidized to oil-soluble asphaltogenic acids. The unsaturated old value a t which injury to apricot leaves becomes just hydrocarbons, per se, are therefore no more toxic to foliage noticeable, it seems reasonable to expect injury to occur with than are the saturates. the use of oil B (unsulfonated residue, 74 per cent) but no The rate of oxidation of the saturated oils a t ordinary injury with A (96 per cent); we would expect oils C (89 per temperatures is so slow that they are chemically inert tocent) and D (92 per cent) to be on the border line. wards foliage. The rate of oxidation of oils containing appreciable amounts of unsaturated hydrocarbons is also Specific Character of Asphaltogenic-Acid very slow in darkness. Sunlight, however, activates the oxidaToxicity tion to a marked degree, and the rate of formation of the toxic acids apparently becomes greater than can be tolerated The toxicity of the asphaltogenic acids to foliage appears t o by foliage. be quite specific. When as high as 5 per cent of stearic and The amount of asphaltogenio acids which a n oil must conoleic acids was dissolved in inert, mineral petrolatum type tain in order to be injurious to foliage was found to be relaoils, no indication of foliage burning either in light or darkness
APRIL, 1936
'
INDUSTRIAL AKD ENGINEERING CHEMISTRY
tively small. Apricot leaves kept in darkness showed no injury from oils containing less than 0.40 per cent of these acids, irrespective of the percentage of unsaturated hydrocarbons present in the oils. With 0.70 per cent, injury became noticeable. The toxic threshold value for apricot leaves is therefore approximately 0.50 per cent acids. Although this value may differ for other kinds of foliage, the indications are that it is always small. The results, obtained in the oxidation tests carried out under the light and moisture conditions somewhat comparable to those found in leaves, indicate that the formation of asphaltogenic acids is roughly proportional to the percentage of unsaturated hydrocarbons present in an oil. We would not expect, however, that all oils with the same unsulfonated residue (i, e., the same amount of unsaturates) would neces-
464
sarily be equally resistant to oxidation in the presence of light. For this reason a test whereby petroleum oils intended for foliage spraying could be examined as to their relative resistance to oxidation in light appears of value.
Literature Cited (1) Gray, G. P., and de Ong, E. R., IXD. ENQ.CHEM.,18, 175-80
(2) (3) (4) (5) (6)
(1926). Haslam, R. T., and Frolich, P. K., Ibid., 19, 292-6 (1927). Knight, Hugh, Plant Physiol., 4, 299-321 (1929). Rohrbaugh, P. W., Ibid., 9, 699-730 (1934). Staeger, H . C., IND.EXG.CHEM.,17, 1272-5 (1925). Young, Paul, Am. J. Botany, 22, 1-8 (1935).
RECBIVED September 24, 1935. Presented before the Division of Petroleum. Chemistry at the 90th Meeting of the American Chemical Society, Sss Francisco, Calif., August 19 to 23. 1935.
Action of Aluminum Chloride on Paraffins Autodestructive Alkylation v. N. IPATIEFF A N D A. V. GROSSE Universal Oil Products Company, Riverside: Ill.
F
OR the understanding and correct interpretation of the reaction of paraffins with olefins in the presence of aluminum chloride (S),a knowledge of its behavior towards paraffins alone was necessary. A number of investigations on the action of aluminum chloride on hydrocarbons have been carried out in the past; the most interesting are recent papers by Grignard and Stratford ( 1 ) and Kenitzescu with his co-workers (6). However, in these investigations no explanation seems to be given of the reactions taking place with paraffins. The present writers believe that they have found a n explanation after their discovery of the reaction of paraffins with olefins which takes place under very mild conditions ( 2 ) . In this paper data on the action of aluminum chloride on n-butane, n-hexane, n-heptane, and 2,2,4-trimethylpentane will be given and discussed. Theoretical Discussion It was found that aluminum chloride acts on all these paraffins. However, the presence of hydrogen chloride is necessary for the reaction, and it can be added either directly or indirectly-for instance, through the addition of water. If every trace of hydrogen chloride and water is eliminated, aluminum chloride does not react to any material extent with the hydrocarbons unless the temperature is raised sufficiently high (about 150" to 200" C . ) to cause the formation of
Aluminum chloride converts paraffins, into a complex mixture of paraffins of. lower and higher molecular weight according to a type of reaction which has been termed 'autodestructive alkylation." The conversion and reactivity of an individual paraffin is dependent on its structure; in general it increases with (a)its molecular weight and ( b )its degree of branching.
hydrogen chloride, owing to a reaction between the aluminum chloride and the paraffin itself. The reaction products consist in all four cases of a waterwhite upper layer and a much smaller red-brown viscous lower layer containing the aluminum chloride, combined with highly unsaturated hydrocarbons; in the case of n-butane the upper layer consists of liquefied gas, stable only undep pressure. n-Butane showed no appreciable change below 100" C.. At 175" during 3 or 4 hours it was converted to a large extent into propane, ethane, and methane and partly isomerized' into isobutane; a t this high temperature the other three. paraffins are completely broken down. The n-hexane was converted in 3 hours a t its boiling point, (69" C.) into higher and lower boiling paraffins to the extent. of 20-25 per cent. With n-heptane a marked reaction took place a t its boiling point (98" C,), and about 35 to 40 per cent is changed in 3 hours. In the case of 2,2,4-trimethylpentane the reaction with. aluminum chloride took place even a t room temperature a n d a t 25" to 50" C. in 3 or 4 hours about 90 per cent of the octane. was converted into lower and higher boiling paraffin hydro-. carbons. From these examples it can be concluded that the reactivityof paraffins under comparable conditions increases both with (a) their molecular weight and (b) their degree of branching. The nature of the reaction becomes clearer if we look a t the products formed. The distillation curve (Figure 1) representing a high-temperature Podbielniak distillation analysis of the upper layer obtained in the case of 2,2,4-trimethylpen--
