[DEPARTMENT OF CHEMISTRY, SYRACUSE UNIVBFt5ITY]
OZONIZATION OF ORGANIC COMPOUNDS C. C. SPENCER, W. I. WEAVER, E. A. OBERRIGHT, H. J. SYKES, A. L. BARNEY, AND A. L. ELDER Received July 8, 19.60
I. VAPOR-PHASE OZONIZATION OF DIPENTENE AND d-LIMONENE
With the exception of patents granted to Knox (1) and Rogers (2) for vapor-phase ozonization of pinene and cinnamic aldehyde, no reports were found in the literature of methods for preparing ozonides in the vapor phase, Such a procedure is an excellent one, for the necessity of separating the ozonides from solvents is eliminated, and also the reactions may be carried out more rapidly than in solution. The rate of ozonization in solution is dependent upon the solubility of ozone in the solvents, but in vapor-phase ozonization the rate is much greater by virtue of the increased concentration of ozone and the unsaturated substance. Only compounds having an appreciable vapor pressure and those forming stable products were ozonized in the present study. The terpenes, dipentene, d-limonene, and &)-pinene, were successfully ozonized in the vapor phase. The chief difficulty in the preparation of ozonides in the vapor state is that the ozonide mists are not easily wetted by solvents. This difficulty has been removed by the use of an electrical precipitator. Furthermore, with the greater concentration of ozone and the increased time of contact, oxidation-reactions other than ozonization may occur. Many different types of ozonizers and reaction-chambers were tried. A description of the most satisfactory apparatus is included in this paper. APPARATUS
Ozone was generated by means of an ozonizer made according to the specificationa of Smith (3). This type of ozonizer gives a higher yield of ozone than others. The dimensions of the ozonizer described by Smith should be closely followed. A glass reaction-chamber, one meter in length and 20mm. in diameter, permits increased time for contact of the reactants. The precipitator was made readily and with very little cost from the outer jacket of a water condenser. The center wire consisted of several strips of galvanized window screen wire. Several of these strips gave many small points for electron discharge to take place rapidly. The lower end of the wire was fastened to a loop on the long end of a T-shaped glass rod. The wire and glass rod were inserted in the lower opening of the condenser jacket and the wire through a cork in the upper opening. The arms of the glass rod were made of suitable length and size to prevent clogging of 610
OZONIZATION OF ORGANIC COMPOUNDS
611
the opening and to permit an Erlenmeyer flask to be placed over the bottom to receive the precipitated ozonides. A strip of copper foil waa wrapped around the outside of the condenser jacket to serve aa the low potential electrode. During operation, 12,000 volts pulsating D. C. waa maintained between the wire and the foil. A small window in the foil aided in controlling the precipitator. Oxygen was supplied from a Linde air cylinder and the pressure kept constant by means of a hydrostat. The oxygen was dried with concentrated sulfuric acid and calcium chloride and then divided into two paths. One led through a calibrated flowmeter and thence through a series of absorption bottlee in which the liquid to be ozonized was placed. The other path led through a calibrated flowmeter and thence through the ozonizer. The two paths were then united in the reaction-chamber, where the ozonides appeared as dense white smokes and were swept along to the precipitator by the excess oxygen. The ozonides were collected in the Erlenmeyer
receiver, and the excess gases passed out of the exit tube a t the top of the precipitator and into a solution of potassium iodide and sodium thiosulfate to destroy any unreacted ozone. To ensure complete ozonization, an excess of ozone was maintained at all times. COMPARISON OF OZONUATION OF DIPENTENE IN SOLUTION AND I N THE
VAPOR STATE
In the vapor phase the reaction of ozone with dipentene yielded a heavy smoke which wm precipitated aa a very viscous, yellow liquid. This product was soluble in alcohol (9573 and the solution gave characteristic reactions of ozonides. Combustion data indicated the formation of the &ozonide in the gaseous state. The reaction probably proceeds according to the following equation.
612
SPENCER, WEAVER, OBERRIGHT,
c / \ HCI
CH2 I
SYKES, BARNEY, AND ELDER
0,-C
-
I/
2oj
\
HCI
H,C-&=CH2
CHz I
&C-&-CH2
\ I 0 3
Dipentene
Dipentene diozonide
An ozonide was formed in the liquid state by dissolving 25 g. of dipentene in 100 g. of heptane. This solution was cooled in an ice-bath as ozone was bubbled through. The ozonide separated as a very viscous, white liquid. The ozone was passed through for ten hours, which was in excess of the time needed for complete ozonization. The excess liquid was decanted, and the ozonide washed with ether and alcohol and then dried under reduced pressure. Combustion data indicated the formation of the monozonide in a heptane solution. &Limonene and ozone react in the gaseous state to form a smoke with properties similar to those described above in the case of dipentene. Combustion data indicated that in the gaseous state ozonization took place yielding the diozonide. Twenty five grams of d-limonene was dissolved in heptane and ozonized like dipentene. Again the combustion data indicated the formation of the monozonide in heptane solution. Citral, pseudoionone, ionone, citronellol, citronellal, terpineol, carvone, geraniol, and isoeugenol were all tried, but these compounds were not volatile enough to produce an appreciable amount of ozonide. COMBUSTION DATA
Ozonide oj dipentene jrm vapor-phase treatment W t . ofsampk
I f .of COS
0.1339 0.2643 .1496 .2940 C ~ ~ I S (theoretical) OS
Wt.of E&
%C
0.0813
53.79 53.59 51.72
.a15
Ozonide of dipentene i n heptane wf. O f 8 W l I p h W f .Ofco; wt.of H& 0.18230 0.4306 0.1396 .1603 .3518 .1193 Ci&eOa (theoretical)
Rapid decomposition.
%E
6.8 6.84 6.90
solution %C
64.95 59.96* 65.21
%E
8.33 8.35 8.70
613
OZONIZATION O F ORGANIC COMPOUNDS
Ozonide of d-limonene from vapor-phase treatment Wt. of sample
Wt. of COz
0.1429 0.2758 ,1275 .2524 Cl&IleOs (theoretical)
Vt.
Ell0
0.0884
.M99
Ozonide of d-limonene i n heptane Wt. of sample
W;. of Cor
0.1483 0.3474 .2593 .6080 C I O H I ~(theoretical) O~
%C
%E
53.7 53.9 51.72
7.01 7.01 6.90
SOhth?~
I t 1 01HI0
%C
%E
0.1127 .1982
63.88 63.94
8.50 8-55 8.70
65.21
11, VAPOR-PHASE OZONIZATION OF a(d)-PINENE
As previously mentioned, patents have been granted to Knox (1) and Rogers (2)for vapor-phase ozonization of pinene but neither reported any proof of the composition of the product obtained. In this laboratory ozone was reacted with a@)-pinenevapor. The product formed by this exothermic reaction appeared as a white mist which, since it was not readily absorbed by any solvent, was collected by a modified Cottrell precipitator. A light yellow, viscous oil was obtained, which showed on analysis five oxygen atoms per molecule of pinene. This product was soluble in alcohol and ether, slightly soluble in petroleum ether, and almost insoluble in water. It showed typical ozonide reactions toward heat, potassium permanganate, and potassium iodide. Hydrolysis of the ozonide proceeded best in alkaline solution, either in alcohol, or more slowly, in water. Hydrolysis in alcohol gave an insoluble white salt which gave with silver nitrate solution and also with hot concentrated sulfuric acid tests indicative of an alpha carbonyl group. In the aqueous basic solution, with three per cent hydrogen peroxide added from time to time, degradation to the salt of the next lower acid occurred, and sodium carbonate was produced. This acid gave a positive iodoform test, and formed a semicarbazone corresponding in nitrogen content and physical properties to pinononic acid semicarbazone. These results can only be explained by the oxidation of the methylene group alpha to the double bond by the slight excess of ozone present during the reaction, and by the oxygen present in the reaction-mixture. Durland and Adkins (4) have shown that such oxidations can take place even during ozonization in solution, and the ketone produced by this oxidation is known (5) to be one of the major products of the oxidation of pinene by atmospheric oxygen. The claims based on the original work (6) on the ozonization of pinene in solution, that pinonic acid is the normal product of hydrolysis, is somewhat questionable, since the analysis figures for the product isolated (the
614
SPENCER, WEAVER, OBERRIGHT, SYKES, BARNEY, AND ELDER
semicarbazone of pinonic acid) agree in nitrogen content for the pinononic acid derivative, while the carbon analysis agrees for pinonic acid semicarbazone. A miscalculation of the theoretical per cent of nitrogen in this article, as well as in the first reported preparation of pinonic acid semicarbazone by Tiemann (7), casts doubt on the validity of the interpretation previously reported. EXPERIMENTAL
Oxygen, dried by bubbling through sulfuric acid, was directed into two paths. One path led through a calibrated flowmeter and then through a series of absorption bottles filled with pinene to saturate the stream with pinene vapor. The other path led through a Siemen's ozonizer, calibrated against potassium iodide. The two patha joined in a reaction-chamber where the ozonide formed aa a white mist which waa precipitated electrically. The product gave the following analyses: W:.oframph
Grama CO:
0.1678 0.3503 .la4 .3441 ClOH1~08 calculated C1&1&4 calculated Cldl1401 calculated CIOHUOS calculated
Grama H t o
%C
0.1119 .lo95
56.93 56.73 65.21 60.00 60.60 56.07
%H
7.46 7.41 8.70 8.00 7.07 6.54
To 3.2 g. of the ozonide, 42 cc. of 0.4 N alcoholic sodium hydroxide was added. A precipitate of 1.5 g. of the sodium salt of the acid was separated and dried. Either the sodium salt, or the free acid obtained from the salt by acidification and extraction, precipitated metallic silver from a silver nitrate solution and gave carbon monoxide when heated with concentrated sulfuric acid. Hydrolysis of the ozonide with aqueous sodium hydroxide and hydrogen peroxide proceeded readily. To 11.4 g. of the ozonide, 4.8 g. of sodium hydroxide in 200 CC. of water was added. The reaction-mixture gradually darkened, but cleared immediately on the addition from time to time of a few cubic centimeters of hydrogen peroxide (3%). After evaporation to dryness, 13.09 g. of mixed sodium salts remained. Very emall amounts of steam-volatile products were removed during the evaporation. Further purification, which was necessary for easy formation of the semicarbazone, was carried out by adding dilute acid to the sodium salts and skimming off a small amount of resinous material which was floated to the surface by the escaping carbon dioxide. Upon extraction of the acid suspeneion with chloroform, the free acid could be obtained as an oil. Attempts to crystallize the acid were unsuccessful. The oily acid distilled from 160" to 195" at 12 mm. pressure. The distillate gave the following analyses: W;.01Sam&
amma COr
0.1783 0.4120 .%38 ,5849 C O H ~ (pinononic ~O~ acid) CZOHl~Ol(pinonic acid)
amma to
0.1309 .18% calculated calculated
%C
63.00 62.85 63.53 65.22
%H
8.20 8.06
8.23 8.70
615
OZONIZATION OF ORGANIC COMPOUNDS
From the oily acid about 46-60oJo yields of the semicarbazone were obtained using semicarbazide hydrochloride and sodium acetate. The semicarbszone, after drying in an oven a t 136", and over phosphorus pentoxide for two days gave the following analyses: O b s n a l duma al Na
Bf.of romnpls
I. 2.842 mg. 11. 3.670 mg. 111. 3.328 mg.
0.463 cc.
%N
(no, 758 mm.) (no, 758 mm.)
calculated
18.16 18.28 18.59 18.50
calculated
17.42
.599 cc. .565 cc. (26", 741 mm.)
CIOHirNaOa (pinononic acid semicarbaEone) CiiHieNiOa (phonic acid semicarbazone)
I t waa impossible to prepare the pinononic acid in a crystalline form even after hydrolysis of the semicarbazone. This may be due to the fact that various stereoieomers of the structure are possible and would be present together even in the h a l product. The evidence thus far would indicate the following possible formulse for the product of the reaction between pinene and ozone in the gaseoue phase. CHa
CH: 01-
I c
I
Oa-C
I/ \
HC
CH
I/ \
HC
CH
\
CHa CHa
O=C
H
H
Verbenone oxozonide
Verbenone peroxide ozonide
Since both would give the same products on hydrolysis, a decision between them cannot be made by this method.
111. OZONOLYSIS OF l,&BUTADIENE
Ozonolysis of unsaturated organic compounds has been employed extensively for proving the location of multiple bonds in a molecule. With the exception of the work of Enklaar (8) on ocimene, ozonolysis of openchain conjugated systems has not been reported. The object of this work was to study the addition of ozone to butadiene, to determine the type of addition. 1,3-Butadiene gave on complete ozoniaation in chloroform solution a
616
SPENCER, WEAVER, OBERRIGHT, SYKES, BARNEY, AND ELDER
1:2,3 :4-diozonide1 soluble in chloroform, which could not be readily isolated due to its great explosiveness. Oxalic acid crystallized from the chloroform solution of the diozonide on standing. Hydrolysis carried out in the presence of chloroform, using the method of Church, Whitmore, and McGrew (9), gave formaldehyde and glyoxal. The monozonide of 1,3-butadiene was prepared by bubbling ozone into a solution of butadiene in petroleum ether. The monozonide was only slightly soluble, and collected as a white amorphous solid in the reactionchamber. Although it is difficult to formulate a mechanism for the hydrolysis of the 1 4-addition-product of ozone to 1,3-butadiene1 it would seem that maleic aldehyde would be a likely hydrolytic product. No indication of maleic aldehyde was found as a hydrolytic product of the monozonide in spite of attempts at isolation through the 2,4-dinitrophenylhydrazone, or by oxidation to maleic acid. Hydrolysis carried out as before, gave acrolein and formaldehyde, indicating 1,3-addition. The monozonide is not explosive. EXPERIMENTAL
Ozone from a Siemens' ozonizer, calibrated against potassium iodide, was precooled by passage through a dry ice condenser and passed into a solution of 1,3butadiene in chloroform or in petroleum ether. The butadiene solution was cooled by an ice-salt-bath, and a dry ice condenser prevented the loss of butadiene. Preparation of the diozonide. Ozone was bubbled into a solution of 12 cc. of liquid butadiene in 200 cc. of chloroform for 8 hours until a blue color was apparent in the solution, the blue color being taken as the end-point of complete ozonization. Hydrolysis of the diozonide. Hydrolysis of the ozonide was carried out by Whitmore's method. Fifty cubic centimeters of the above chloroform solution waa added to 200 cc. of water. A few drops of silver nitrate solution and about 4 g. of zinc dust were introduced. Hydrolysis took place immediately, even in the cold. After hydrolysis, the chloroform and water layers were separated. The chloroform layer contained very little of the products. The water layer gave positive color tests for formaldehyde and gave a large amount of methylenedi-p-naphthol, m.p. 189-192" (decomp.). The water solution also gave glyoxal 2,4-dinitrophenylhydrazone m.p. 327" (corr.). The chloroform solution of the ozonide deposited oxalic acid crystals on standing (m.p. 101", anhydrous 189'). Preparation of the monozonide. Twenty cubic centimeters of liquid butadiene was dissolved in 200 cc. of petroleum ether, and ozone was bubbled in for 6 hours. The ozonide formed as a white, semi-solid material. Hydrolysis of the monozonide. The hydrolysis was carried out as before. The petroleum ether was distilled from the solution and from the distillate a 2,4-dinitrophenylhydrazone was obtained (m.p. 156-158'), which gave no lowering of melting point when mixed with known acrolein 2,4-dinitrophenylhydrazoneand gave the melting point 130-135" with the known formaldehyde derivative. From the water solution a 2,4-dinitrophenylhydrazone was obtained (m.p. 153-154'). It gave no lowering on mixed melting point with the known formaldehyde derivative and the melting point 132-136' with the known acrolein derivative. No evidence of any other products was found.
OZONIZATION O F ORGANIC COMPOUNDS
617
SUMMARIES
I Ozonization in the vapor phase is an excellent method for preparing ozonides of organic compounds having an appreciable vapor pressure and forming stable ozonides. The apparatus used is described. The ozonization of dipentene and d-limonene in the gaseous state yields the diozonides.
I1 1. The ozonization of pinene in the vapor phase results in the oxidation of the methylene group alpha to the double bond as well as in the addition of ozone to the unsaturated linkage. 2. Errors in the literature in the calculation of the nitrogen content of pinonic acid semicarbazone have been pointed out.
I11 1. Ozone adds 1:2,3:4 to 1,3-butadiene to form a diozonide and 1,2 to form a monozonide. The diozonide is v e v explosive on warming. The monozonide is relatively stable. 2. No evidence of 1,Paddition of ozone could be found in the monozonide. SYRACUSE, N. Y. REFERENCES
(1) KNOX,U.S. Patent, 1,086,372(Feb. 10, 1914); 1,086,373 (Feb. 10, 1914). U. 5. Patent, 1,924,805(August 29, 1933). (2) ROGERS, (3) SMITE,J . A m . Chem. SOC.,47, 1844 (1925);SMITEAND ULLYOT, J . Am. Chem. SOC., 66, 4327 (1933). (4) DURLAND AND ADKINS,J . A m . Chem. Soc., 61,429 (1939). (5) BLUMANN AND ZEITSCHEL, Ber., 46, 1178 (1913). AND NERESHEIMER, Ber., 41, 38 (1908). (6) HARRIES AND KERSCEBAUM, Ber., 33, 2664 (1900). (7) TIEMANN (8)ENKLAAR, Rec. truo. chim., 27, 423 (1908). (9) CHURCH, WHITMORE,AND MCGREW, J . Am. Chem. Soc., 66,176 (1934).
