[CONTRIBUTION NO. 74 FROM
THE
CHEMISTRY LABORATORY O F THE UNIVERSITY O F UTAH]
ORGANOBORON-NITROGEK COMPOUNDS. 111 (1, 2). THE REACTIONS OF p-ANISIDINE, BENZYLAMINE, AND NITROBEKZENE WITH BORON CHLORIDE CORLISS R. KINNEY'
C; LYKN MAHONEY2
AND
Received July 10, f9.j.3
The study of organoboron-nitrogen compounds has been continued with panisidine and benzylamine. The former reacts with boron chloride as other aromatic amines have been found to react, but benzylamine shows certain differences in behavior. Surprisingly enough, nitrobenzene, although not an amine, reacts with boron chloride and the results of this work have been included. The reaction of p-anisidine with boron chloride takes place readily, but the addition compound or salt formed easily loses hydrogen chloride, and difficulty was experienced in obtaining the pure compound by this method. The best procedure was to treat a cold suspension of p-anisidine hydrochloride in benzene with boron chloride. Under these conditions the boron chloride displaced the hydrogen chloride and the new salt was obtained pure (1). CH30CeK4NHz.HCl
+ BC&
CH30CeH4NH2.BCla
+ HCI
The salt loses two molecules of hydrogen chloride by heating in boiling benzene. The product is a trimer and was named tri-p-anisyltrichlorotriboron nitride. The cyclic structure below was assigned to the substance, following the practice established in the first paper (1). Ca €140C&
I
Tu'
/ \
CIB I
BC1 I
I
c1 The substance is hydrolyzed by cold water apparently to the corresponding hydroxyl derivative. With boiling water both compour,ds are completely hydrolyzed to anisidine and boric acid. By heating boron chloride with an excess of p-anisidine, boric tri-p-anisidide is obtained. BC&
+ GCH30CsH4NHz + B(NHC6H40CHS)a + 3CH30CeH4NHz HC1 *
1 Present address : Department of Fuel Technology, The Pennsylvania State College, State College, Pennsylvania. Present address: Mallinckrodt Chemical Works, St. Louis, Missouri. f
526
ORGANOBORON-NITROGEN COMPOUNDS
527
This substance is relatively air-stable, but is rapidly hydrolyzed by boiling water to boric acid and anisidine. The compound reacts with dry hydrogen chloride in cold benzene solution, forming a white precipitate. This appeared to be a mixture of aaisidine boron chloride and anisidine hydrochloride formed by the following reaction. B(NHCslS40C€I3)3
+ 5HC1 + C H ~ O C ~ H ~ N.BC& H Z + ~ C H ~ O C ~ H ~HC1 NHZ
Aliphatic amines react with boron chloride as well as aromatic amines, but difficulty has been experienced in isolating pure products. With benzylamine, however, more promising results were obtained. The reaction of this amine with boron chloride gave a good yield of the addition compound. The salt when heated lost two moles of hydrogen chloride in the usual may, but the expected trimeric product could not be isolated. Neither was it found possible to isolate boric tribenzylamide by the action of an excess of benzylamine on boron chloride, In view of these difficulties experienced with the aliphatic amines, it appears doubtful whether this method can be extended to include the preparation of the aliphatic boron-nitrogen compounds. As a result of attempting to find a suitable solvent for certain organoboronnitrogen compounds, it was observed that nitrobenzene forms an addition compound with boron chloride. Apparently aluminum chloride forms a similar compound with nitrobenzene (3), but such a derivative has not been reported with the boron halides, although a large variety of boron halide addition compounds are known. The new substance is well crystallized, but is low-melting. It ciecom poses into the original components slightly above the melting point. As might be expected it is extremely reactive and is rapidly decomposed by moisture in the air. Assuming that the boron chloride has formed a salt with an electron pair of the nitro group, the following structure is proposed.
+
c1
:G: B T C1 .. ..
CeH5 : N ..
:o:
.*
c1
EXPERIMENTAL
The salt of p-anisidine and boron chloride, C H ~ O C ~ H I NBCES. U ~ . Twelve grams (0.102 mole) of boron chloride was distilled into 100 g. of pure sodium-dried benzene contained in a 500-mi. two-necked flask equipped with a mercury-sealed stirrer and a dropping-funnel. The solution was stirred vigorously and cooled with an ice-bath while 9 g. (0.073 mole) of p-anisidine dissolved in 100 g. of benzene was dropped in during 1.5 hours. The contents of the dropping-funnel were protected by a calcium chloride tube. After the addition was complete, the cooling-bath was removed and the solution allowed to come to room temperature. A small quantity of solid had precipitated and the liquid had a pink color. About 10 minutes after filtering the solution crystallization set in, forming slightly pink plate-like crystals. These were filtered out, washed with dry benzene and with petroleum ether. After drying 15 minutes in a vacuum desiccator, the crystals were analyzed for boron and chlorine in the usual way by decomposition with water (1). This left a small white residue which resisted even boiling water. Consequently, the analyses were too low. The waterinsoluble material appeared to be a mixture, possibly of the tri-p-anisyltrihydroxytriboron
528
C.
R. KINNEY AND C. L. MAHONEY
nitride and boric tri-p-anisidide. It was not practicable to purify the substance by recrystallization because warming resulted in the loss of hydrogen chloride. After considerable experimentation, the best method found for making the salt was by the displacement of hydrogen chkoride from anisidine hydrochloride. Five grams (0.031 mole) of p-anisidine hydrochloride was suspended in 200 ml. of pure dry benzene. The mixture was cooled with an ice-bath and 16 g. (0.136 mole) of boron chloride distilled into the benzene during 30 minutes. The mixture was stirred cold for an hour then allowed t o warm t o room temperature. During this time the anisidine hydrochloride had been changed into small plate-like crystals. These were removed, washed with benzene and with petroleum ether, and dried in a vacuum desiccator. When treated with water no solid residue remained, as with the first preparation described, but a film of liquid was observed on the water. By heating the salt in a sulfuric acid-bath a t 120" for 5 minutes a colorless liquid distilled out, which was condensed and was identified as benzene by nitration and identification of dinitrobenzene by mixed melting point. A sample of the salt weighing 0.4398 g. lost 0.0646g. of benzene which showed that the salt contains 0.5 molecule of benzene of crystallization. Taking this information into consideration the following analytical data were obtained. Anal. Calc'd for C7HpBClsNO-O.SC6Hs: B, 3.87; C1, 38.07. B, 3.86, 3.88, 3.91; C1, 37.74, 37.35, 37.83. Found : The salt softened a t 105" and melted a t 108", when heated slowly. Above 112", gas was evolved. When heated rapidly the salt softened a t 105" as before but suddenly melted with gas evolution a t 110'. The substance could not be recrystallized from boiling benzene because of decomposition. The gas evolved was shown t o be hydrogen chloride containing no boron chloride. On heating 0.1219 mole of the salt, 0.247 mole of HC1 was obtained, which shows that two moles of hydrogen chloride were evolved per mole of salt. Tri-p-anisyltrichlorotriboronnitride, (CHsOCJf4NBCl)s. A 3.4-g. (0.014 mole) sample of the salt of anisidine and boron chloride was heated in 100 g. of boiling benzene until no more hydrogen chloride was evolved. This required a total of 18 hours. The solution was concentrated t o 50 ml. and allowed t o cool. The product crystallized in small cubic crystals having a slight yellow color. A t times, a jell formed from which crystals could not be obtained. The crystalline product was washed with benzene and petroleum ether, then dried in a vacuum desiccator. This compound, also, was found to crystallize with benzene of crystallization. An 0.8954-g. sample lost 0.1230 g. of benzene when heated. The molecular weight in freezing benzene was found t o be 570, showing the trimeric nature of the substance. Using this information, the analytical data obtained compare with the theoretical as follows: Anal. Calc'd for ( C I H ~ B C ~ N O ) ~ . CB~, H 5.60; ~ : C1, 18.29; Mol. wt., 580. B, 5.67, 5.60; C1, 18.36, 18.46; Mol. w t . , 570. Found : The compound melted in a sealed capillary tube a t 229-235" with the evolution of gas and formed a dark red liquid, A sample of the substance placed in cold water was changed in crystalline form, and chloride ion was detected in the water. The product melted a t 95115". The only method found for purifying the substance was to dissolve it in the minimum of cold alcohol followed by dilution with water. This resulted in a large loss of material, but raised the melting point to 112-120". When warmed with benzene or alcohol the compound dissolved, but no products were isolated, indicating further decomposition. This instability was further demonstrated during the preparation of one sample which suddenly decomposed a short time after being filtered from the a a t e r . In this case the products were anisidine and boric acid, showing that complete hydrolysis had occurred. The crude compound was found t o contain 6.6% boron as compared with the calculated value of 7.1% for the trihydroxide, (CHSOCJLNBOH)~. Boric tri-p-anisidide, (CHaOCJfrNH)&. An ice-cold solution of 11 g. (0.094mole) of boron chloride in 100 g. of dry benzene was placed in a 500-ml. two-necked flask and stirred while 60 g. (0.48 mole) of p-anisidine dissolved in 100 g. of dry benzene was slowly added over a period of two hours. A t first a large amount of heat was liberated as the amine
ORGANOBORON-NITROGEN COMPOUKDS
529
enrered the boron chloride solution, and a white precipitate formed which rapidly redissolved. (Soona permanent precipitate remained which increased in amount as the reaction progressed. After all of the amine had been added the ice-bath was replaced by an oilbath heated to 120" and the mixture refluxed for 6 hours. The stirring was continued to minimize bumping. The mixture was filtered rapidly while hot and the solid residue extracted with two 75-ml. portions of boiling benzene. The benzene solution was concentrated t o 100 ml. and allowed to cool to room temperature. Upon seeding the solution, crystallizntion proceeded smoothly. -44576 yield of pure cubic crystals vas obtained, based upon the boron chloride used. The mother liquor yielded more of the product, but of less purity. The pure compound gave tests for boron and nitrogen, but not for chlorine. Anal. Calc'd for (CILOCaH&H)3B: E, 2.86. Found: B, 2.83, 2.87, 2.87. Thc melting point of boric tri-p-anisidide was found to be 126". On cooling, the melt did not solidify, indicating decomposition. The compound when kept in a desiccator slowly decomposed, liberating crystals of anisidine which sublimed on to the container walls. It is not clear whether sufficient moisture was available in the air in the desiccator for hydrolysis, or whether the decomposition proceeded with the formation of a boric imide, but either reaction would account for the formation of anisidine. (CHaOCsH4NH)aB
+ HOH
(CHaOCeH4NH)aB +
+ CH30CeHaNHz CHaOCeHiNHB = NCeHdOCHa + CHsOCeH,NH, +
(CHaOCsH4NH)zBOH
Boric trianisidide in benzene solution reacted readily with dry hydrogen chloride, forming a white precipitate. The hydrogen chloride was absorbed quite completely a t first, but more slowly as the reaction progressed. In one experiment the gas was passed into the solution for 10 hours. The product was washed with dry benzene and with dry petroleum ether. It gave qualitative tests for boron, nitrogen, and chlorine. When placed in water a part of the material reacted violently, behaving like the addition salt of anisidine and boron chloride. The remainder of the material dissolved more slowly and behaved like anisidine hydrochloride. T h e salt of benzylamine and boron chloride, CJIsCH2iVH2.BCl~.Nine grams (0.084 mole) of benzylamine dissolved in 100 ml. of dry benzene was slowly added to 13.5 g. (0.115 mole) of boron chloride dissolved in 150 ml. of dry benzene contained in a 500-ml. two-necked flask cooled in ice. The mixture was stirred vigorously throughout the addition to minimize local excess of amine. A white precipitate began t o form immediately and increased in quantity as the reaction progressed. The product was filtered rapidly in a current of dry air, washed with dry benzene and stored under dry benzene. The yield vas 8570 based on the amount of amine used. Attempts to recrystallize the substance failed. When warmed with dry benzene, decomposition set in a t 38" and only a small amount of product dissolved below that temperature, By using the dilute solutions indicated above, the product was sufficiently pure to give the analytical data following. Because of the basicity of benzylamine i t was found necessary to distill out the amine with steam before titrating the boric acid. The chloride ion was determined gravimetrically as silver chloride. C ~4.82; ~ : C1, 47.44. .LnaZ. Calc'd for C ~ H ~ C H , N H Z B B, B, 4.79, 4.55, 4.799; C1, 47.60, 47.65, 48.30. Found : Benzylamine-boron chloride melted in a sealed tube a t 166-167" to a colorless liquid which solidified a t 158"and remelted again a t 166-167". This was repeated three times, indicating that the substance is unusually stable, considering its behavior in benzene solution. Above 185" gas was evolved and the material darkened. When heated with dry benzene, 0.00595 mole of the compound required 0.01157 equivalent of base t o neutralize the hydrogen chloride evolvod. This demonstrated that two moles of hydrogen chloride are evolved per mole of salt. On concentrating the benzene solution, the expected trimer (C6HsCH2NBCl)a was not obtained. A small quantity of needles crystallized out, which on standing soon changed to
530
C. R. K I N N E Y A N D C. L. MAHONEY
small plates. These contained too little boron and too much chlorine to be any simple derivative that might be expected. A n a l . Found: B, 3.42, 3.45; C1, 28.77, 29.86. Because of the small yield of this product nothing further was done with it. Further concentration of the benzene mother liquor failed to yield any additional crystalline material. Reaction of a n excess o j benzylamine on boron chloride. I n an attempt to prepare boric tribenzylamide, 10 g. (0.085mole) of boron chloride dissolved in 100 ml. of dry benzene was treated with 55 g. (0.0514 mole) of benzylamine dissolved in 100 ml. of dry benzene. The reaction flask was cooled with ice during the addition of the amine and stirred constantly. A precipitate formed which was probably the salt of the amine and boron chloride After all of the amine had been added, the mixture was refluxed for as long as 18 hours, in an attempt to complete the reaction. The mixture vias filtered hot, and the precipitate extracted with several small portions of boiling benzene. The residue gave qualitative tests for chlorine and nitrogen, but not for boron. The melting point was 255", which is the melting point of pure benzylamine hydrochloride. These data indicate that the desired reaction was complete. The benzene solutions were concentrated to 150 ml., and after several days one gram of crystals was filtered out. This material was recrystallized from benzene, and melted sharply a t 145". On cooling and remelting, the melting point was again 145". The substance gave a qualitative test for nitrogen, but not for boron or chlorine. The compound was insoluble in water, dilute acid or base, but soluble in concentrated sulfuric acid. The molecular weight was 250. These data were insufficient to identify the substance and since i t was not the compound desired, additional work on i t was discontinued. Further concentration of the benzene solution left an oily residue from which no pure compound could be crystallized or extracted. The reaction was also carried out in boiling xylene. I n this experiment none of the substance melting a t 145" was obtained. The product was a yellow-brown glass from which no pure substance could be obtained. Qualitative tests for boron, nitrogen, and chlorine were obtained on the material. T h e salt of nitrobenzene and boron chloride, C6H6NO~-BCls. A 47.5-g. (0.386 mole) sample of pure freshly distilled nitrobenzene was placed in a 125-ml. Erlenmeyer flask and cooled in an ice-bath. The 5ask was fitted with a stopper bearing a tube which reached nearly to the surface of the nitrobenzene. The tube was connected to a source of boron chloride and 11.5 g. (0.098 mole) was distilled into the nitrobenzene. A t this point the 5ask was shaken slightly and the entire mass solidified. On warming t o room temperature a portion of the material liquefied leaving a mat of fine yellow needles. The product was extremely sensitive to the air, and was liquefied on two or three minutes exposure. Consequently, no attempt was made to determine the yield or to recrystallize i t , The substance gave a positive test for boron, nitrogen, and chlorine. For analysis the crystals were filtered rapidly with suction and washed with dry petroleum ether. The crystals were dried in oacuo by inserting a stopper in the funnel and applying suction. The substance was then hurriedly weighed into dried weighing-bottles and decomposed with water. A n a l . Cal'd for CBHbBCl3KO2:B, 4.50; C1, 44.26. Found : B, 5.33, 7.10; C1, 40.2, 39.2. The salt melted a t 45-47' in a sealed tube to a clear yellow liquid. On cooling and remelting, the melting point WBS again 45-47". On heating to 50.5" bubbles appeared indicating dissociation of the salt. The compound was decomposed violently by water, producing nitrobenzene, boric acid, and hydrogen chloride. A similar reaction was also observed with ethanol. SUMMARY
1. The salt of p-anisidine and boron chloride has been prepared. When heated it lost two molecules of hydrogen chloride and formed tri-p-anisyltrichlorotri-
ORGAXOBORON-NITROGEN COMPOUNDS
53 1
boron nitride. This substance reacted with cold mater to form the corresponding hydroxyl derivative. 2. Boric tri-p-anisidide has been prepared. 3. The salt of benzylamine and boron chloride has been obtained. This salt lost tn-o moles of hydrogen chloride, but no other product could be isolated. 4. Boron chloride was found to combine with nitrobenzene forming a lowmelting substance. This is believed to be a salt of boron chloride with an electron pair. in the nitro group. SALTLAKECITY,UTAH REFERENCES
(1) JOKESAND KINNEY,J . Am. Chem. SOC.,61. 1378 (1939). (2) KINNEYAND KOLBEZEN, J . Am. Chem. Soc., 64, 1584 (1942). (3) ULICH, 2. physik. Chem., Bodenstein-Festband,423 (1931).
