(3) Belcher, R., Bhatty, M. K., Mikrochim. Acta 1956, 1183. (4) Belcher, R., West, T. S., William, M., J . Chem. SOC.1957,4323. (.5 .) Daudt. H. W., J . Sssoc. Oflic. Aar. Chemists 4, 366 11921). (6) Dennis, L. M., Koller, J. P., J . Am. Chem. Soc. 41. 949 - ~ (1919'i. ( 7 j Foot,-H. %., Ibid., 60,'1349 (1938). ( 8 ) Kolthoff, I. M., Law, A., 2. Anal. Chem. 73, 177 (1928). I
I
\ - - -
(9) Kolthoff, I. M., Stenger, V. A., IND. ENG.CHEM.,ANAL.ED. 7, 79 (1935). (10) Marcali, K., Rieman, W., Ibid., 18, 709 (1946). ( 1 1 ) Palmen, J., Finska. Kemistsamfundets M e d d . 42, 46 (1933). (12) Ibid., 43, 151 (1934). (13) Rupp, E., Rossler, E., Arch. Pharm. 243, 104 (1905).
(14) Tomicek, O., Jasek, M., Collection Czech. Chem. Comm. 10, 353 (1938). (15) Tomicek, O., Jasek, M., J . Am. Chem. SOC.57,2409 (1935). (16) Willard, H. H., Cake, W. E., Ibid., 42, 2646 (1920).
RECEIVED for review December 11, 1961 Accepted -4pril 16, 1962.
Differentiation of Organic Acids and Phenols by Heating with Metal Halides PING-YUAN YEH, LUNG CHING LIN, SHU-SHU YANG, and SHU-MIN CHEN Deparfmenf of Chemistry, National Taiwan University, Taiwan, China
b The reaction reported for microanalysis of certain organic acids and o-nitrophenol (by heating with NaCl was reat 160' C. to give HCI investigated. Passage of steam into the hot reaction mixture of acids and sodium chloride turned the negative reactions to positive ones (HCI ), which were further accelerated b y employing calcium chloride dihydrate in the place of sodium chloride. Phenols failed to give hydrogen chloride even when heated with calcium chloride. Calcium chloride also showed catalytic action similar to aluminum chloride.
r)
I
has been reported b y Feigl and Stark-hfayer (6) that when o-nitrophenol was heated with sodium chloride at 160" C. hydrogen chloride was produced. This reaction was recommended by the same authors as a characteristic reaction of o-nitrophenol and might be applied to distinguish i t from the meta and para isomers, since the latter two isomers did not give the same results. Dicarboxylic acids (oxalic, malonic, succinic, adipic, pimeric, azelaic, malonic, and tartaric acids), polycarboxylic acids (citric acid), and certain aromatic acids (benzoic, cinnamic, phenylacetic, mandelic, salicylic, and phthalic acids) also showed the above reaction. The detection of the released hydrogen chloride by indicator paper or by the demasking of silver ferrocyanide made possible a procedure for microanalysis. On the other hand, aliphatic monocarboxylic acids, hydroxamic acid, and sulfonic acids were negative in this reaction. From these results Feigl and Stark3layer concluded that this reaction could hardly be considered as based on the acid strength of the acids or phenols. It appears that the active acids are far stronger acids a t 160" C. than when disT
990
ANALYTICAL CHEMISTRY
solved in water or other solvents (6). An alternative explanation of this reaction was that sodium chloride might be electrostatically attracted on the surface of the solid acid to accelerate elimination of a proton ( 5 ) . A. radical mechanism has also been proposed ( 5 ) . Being highly interested in Feigl's special lecture ( 5 ) ,we reinvestigated the above reaction, and found that o-nitrophenol did not give even a trace of hydrogen chloride when heated with sodium chloride at 200" C. A small amount of sublimed o-nitrophenol might cause the false positive result (HC1 ) because of its acidity when tested with indicator paper. We also confirmed t h a t maleic, malonic, and adipic acids, on heating with sodium chloride, gave hydrogen chloride which rms identified by converting it to the silver chloride precipitate using a silver nitrate trap. Both phthalic and salicylic acids have the same pK, 3.00 ( 7 ) ,and the former is positive while the latter is negative. Since the formation of a large amount of phthalic anhydride was noted in the reaction with phthalic acid, there seemed a distinct possibility that the gaseous water molecules liberated from the acid TI ere essential for the reaction to proceed. Comparison of the acids which gave positive reactions with those which gave negative results revealed
/COOH CeH4' 'COOH /COOH CsH, 'COOH ,COOCBH4 'COOH
/co\
the fact that the former afforded water on heating, while the latter did not release water when heated. Strong evidence for the necessity of water vapor in the reaction u-as obtained by passing steam directly into the heated mixture of benzoic acid and sodium chloride to turn the negative reaction into positive one-Le., to give hydrogen chloride. Finally, the crystalline water in calcium chloride was utilized as the source of steam a t elevated temperatures to bring about the above reaction, while calcium chloride itself was substituted for the role of sodium chloride in the reaction. Thus benzoic acid furnished about one hundred times as much hydrogen chloride as that obtained when steam was passed into the corresponding mixture with sodium chloride while heating. The use of calcium chloride instead of sodium chloride in the reaction with oxalic, maleic, or malonic acid yielded, as expected from the above considerations, almost the same amount of hydrogen chloride as when sodium chloride was employed. This suggested t h a t water vapor produced from the dicarboxylic acid on heating played the same role as the crystalline water in calcium chloride. The reaction mechanism of the above reaction (with phthalic acid as a n example) may be expressed as follows:
Since hydrogen chloride was removed readily from the reaction mixture at 160" C., the above mechanism, which involved a contradiction t o a general conception t h a t a stronger acid(HC1) may liberate the weaker acid (pathalic acid) from its salt, may proceed to some extent. T o establish the above mechanism, isolation of the sodium salt of the acid from the reaction mixture mas tried unsuccessfully. This difficulty was overcome b y utilizing the above discovery, Le., the reaction of palmitic acid with calcium chloride. Palmitic acid, when heated with sodium chloride, did not give even a trace of hydrogen chloride. However, on heating palmitic acid ith calcium chloride, the formation of hydrogen chloride was observed and, although calcium palmitate dissolved in palmitic acid to some extent, calcium palmitate was readily isolated from the reaction mixture in 23.7% yield. It is seen from Table I t h a t phenols did not give a positive reaction even when heated with calcium chloride, showing t h a t acid strength is another factor in the reaction under consideration. Thus this reaction may be utilized as a test to differentiate acids from phenols, except phenols with a high pK,
such as picric acid (pK, 0.8) which give a positive reaction. T h e melting points of acids and phenols, as given in Table I, however, have no apparent effect on the reaction. An attempt was made t o turn the negative reaction in the case of the mixture of phenol with calcium chloride into positive (HC1 t ) by adding iodine to the mixture. As expected, the evolution of hydrogen chloride mas identified by the formation of silver chloride precipitate. The product produced in the reaction flask, however, was shown to be 4-iodophenol (12). Aromatic iodination of phenols occurs in the presence of alkali and oxidizing agents, such as iodic acid, mercuric oxide, and hypoiodous acid (from iodine and alkali) (1,2). The presence of alkali also converts free phenols into phenoxide ions, which undergo electrophilic substitution more rapidly than phenols. In this work the iodinations of phenol and resorcinol were brought about in the absence of alkali and any oxidizing agent, b y means of calcium chloride and iodine. If the reaction, CaClz 1 2 + CaIz Cl?, occurs during the above reaction, phenol might be chlorinated b y chlorine followed b y replacement of the chlorine atom by a n iodine to give 4-iodophenol.
+
+
+
However, the reaction, CaC& 1 2 .-t CaIz Clz, is well known to proceed in the reverse direction. A test with calcium chloride and iodine under the same experimental condition showed that neither chlorine gas nor hydrogen chloride was produced. The possible formation of calcium chloroiodide from calcium chloride and iodine a t about 400' C. has been reported ( 9 ) . If the reaction, CaClz Iz +CaICl ICl, proceeds, the iodochloride formed would readily react with phenol to afford 4-iodophenol. On heating calcium chloride with iodine as mentioned above, however, hydrogen chloride should readily be produced from the reaction of low boiling iodochloride (b.p. 97" C,), if produced, with water as H,O + HC1 HIO. follo\vs: IC1 In fact, this was not the case. The above iodination might proceed according to the following scheme:
+
+
+
+
+
CaC12 Phenol
H+
If
+ I+
+
-
-.f
[ICaClZl4-iodophenol
+ [ICaClz]-
-.f
+
I+
+ H+
CaICl $- HCl
So far as we are aware, no one has reported the Friedel-Crafts reaction catalyzed with calcium chloride nor any complex ion of calcium such as [ICaClJ-.
Table 1.
Reaction of Sodium Chloride (or Calcium Chloride Dihydrate) with Acids and Phenols Acids and Phenols Grams AgCl ( % yield) Formed in Feigl and AgNO8 Trap in Reaction with Stark-Mayer ___ 1f.p. PK5 Results ( 6 ) SaCl XaC1 and steam CaCl?.2H20 ( " C.) (7) Yame Oxalic acid dihydrate 187 1.23 8 . 0 (55.8) Positive 7.9 (55.1) 1Ialeic acid 7 . 3 (50.9) 130 1.9 Positive 6 . 9 (48.1) f-Nitrobenzoic acid 148 2.17 6 . 9 (48.1) None 0 . 2 (1.4) ~3,5-Dinitrobenzoicacid 205 2.80 None 6 . 0 (41.8) Malonic acid 135 2.80 Positive 6 . 4 (44.6) 5 . 9 (41.2) 0.2 (1.4)* 191a 3.00 Positive 0 . 2 (1.4)b Phthalic acid Phthalic anhydride Xone Trace Salicylic acid 159 3.00 Positive Sone 6 . 3 (44.0)" 0 . 1 (0.7) 287 3.00 Fumaric acid 5 . 8 (40.4) None Benzoic acid 122 4.17 Positive Noned 6 . 1 (42.6)a 0.065 (0.5) Succinic acid 185 4.19 Positive 6 . 1 142.6) 5 5 (38 Phenylacetic acid 78 4.31 Positive None hdipic acid 151 4.43 Positive 5 0 (34 6) Cinnamic acid 136 4.44 Positive Sone hTegative Palmitic acid 63 5.20 (10) None Potassium biphthalate 5.28 Nonef Negative Stearic acid 70 5.36 (3,11) None :Potassium bisuccinate 5.64 None Phloroglucinol 219 7.0 None ' Xone None p-Nitrophenol 114 7.16 Kegative None Sone o-Ntrophenol 45 7.21 Positive None' 8.0 Negative rn-Nitrophenol 96 Sone h'one Resorcinol 110 9.4 Xone Nonej Phenol 43 10.01 Xone None$ 2,4-Dinitrochlorobenzene None None a Heated in sealed tube. Low yields were possibly caused by formation of the anhydride. PreciDitation of AeCl started at 150" C. * Small amount of bYenzoic acid sublimed and deposited on neck of the flask, but not in side tube. No precipitate formed when an aqueous solution of benzoic acid was mixed with AgNOa solution. 0 Heated to 180" C. f Heated to 220' C. HC1 formed a t 150" C. * Precipitation of AgCl started and proceeded rapidly when heated a t 125" and at 145' C., respectively, while condensation of water in side tube of flask was observed a t 132" C. Some yellow o-nitrophenol sublimed and condensed on neck and side tube of reaction flask. i In presence of calcium chloride and iodine, resorcinol and phenol gave, respectively, 3.3 grams (23.0% yield) and 3.0 grams (20.9% yield) of AgCl in the AgN03 trap.
VOL. 34, NO. 8, JULY 1962
0
991
The presence of this complex ion was established as follows: Benzoyl chloride and mesitylene, the boiling point of which (165" C.) was close to the reaction temperature in the above reactions, was heated separately 11ith aluniinuin chloride and calcium chloride. The formation of durene, n hich could be isolated readily by taking advantage of its high melting point, waq confirmed in both cases. Since methyl chloride could not he isolated from the reaction product of mesitylene n-ith benzoyl chloride or mesitylene with aluminum chloride alone (41,and durene, isodurene, and xylene w r e obtained from the reaction of mesitylene, aluniinum chloride, and hydrogen chloride gas a t 150" to 160" C. (S), the niechaniw involved in the reaction n i t h calcium chloride and benzoyl rhloride may be expressed as qtarting from the formation of the calcium complex ion from a trace amount of hydrogen chloride and calcium chloride as follons:
hours and then kept a t t h a t teniperature for a n additional hour. I n some euperiments, the acid and sodium chloride were gradually heated, while a mixture of steam and air was passed into the mixture a t a rate of 2 nil. per second. The amount of steam was so regulated that as the water condensed in the side tube of the flask, there was almost the same amount as in the reaction of phthalic acid. The silver chloride precipitate which n a s formed in the trap was filtered through a sintered-glass filter and washed successively with n a t e r containing a little nitric acid, nater, dilute alkali, water, and alcohol. The precipitate was dried a t 100" C. and finally a t 130" C. and weighed. Blank Tests. Sodium chloride and calcium chloride dihydrate, when heated alone as above to 180' a n d 160' C.. respectively, did not give any hydrogen chloride. Calcium chloride dihydrate (14.7 grams), however, afforded 6 mg. of silver chloride precipitate on heating a t 180' C. for 2
CaC12 + HC1 +. [ClCaCl?]C HB
+ H+
H CHS
IA
I
f)
+ HC1 + CaCh + CH3+
A
Thus the presence of the calcium complex ions, [ClCaCl,]- and [ICaC12]-, a t 170" C. in the reaction under discussion seems plausible. EXPERIMENTAL
Reagents. Most of t h e chemicals used i n this work n e r e analytical grade and extra pure. When reagent grades h e r e used, they were redistilled or recrystallized. Sodium chloride was dried a t 150' C. for 3 hours before use. Apparatus. A current of air, passed through a soda lime tube (to remove carbon dioxide) and a sulfuric acid wash bottle at t h e rate of 3 bubbles per second, was led through a n inlet tube with small holes a t its end into a well mixed mixture of a n acid (or a phenol) and a halide heated in a glycerol bath. I n general, 0.1 mole of organic acid and 0.1 mole of either sodium chloride or calcium chloride dihydrate were used. The exit air carrying hydrogen chloride produced in the reaction was passed through a trap containing 50 nil. of 30y0 silver nitrate solution. Experimental Procedure. T h e temperature of t h e reaction mixture was raised gradually from room ternperature to 170" C. within a period of 1.5
992
ANALYTICAL CHEMISTRY
hours. The same results n e r e obtained when steam was passed into the chlorides during the heating Oxalic Acid and Sodium Chloride. Silver chloride precipitate began t o appear in t h e silver nitrate t r a p TT hen a mixture of oxalic acid and sodium chloride was heated to 90" C. Some oxalic acid crjstals condensed on t h e neck of the flask a t 100' C. and the condensation of water in t h e side tube of the flask v a s observed a t 125" C. The amount of silver chloride precipitate obtained was 7.9 grams. I n another run, heating was continued to investigate the formation of carbon dioxide resulting from the deconiposition of oxalic acid. The carbon dioxide, which evolved a t 190" C., was converted into barium carbonate. When oxalic acid alone was heated in the same way as above to 170" C. as a blank test, the gray precipitate obtained weighed only 40 mg. Phthalic Acid and Sodium Chloride. JVhen a mixture of phthalic acid and sodium chloride was heated to 132"C., phthalic anhydride crystals started t o appear on the neck of the flask, and silver chloride began t o precipitate at 140" C., while water condensed on
the side tube of the flask n-hen the temperature reached 180°C. At 19O"C., the reaction mixture started to mrlt and was dehydrated vigorously. The dehydration ceased within 15 minutes. Then the niixt'ure \vas kept at' 190" C. for 2 more hours. The phthalic anhydride deposited on the neck of the flask n-eighed 9.2 grams. The rcactioii products were extracted n-ith 100 nil. of rvater and filtcwd to give 4.4 grams of residue (phthalic.acid and it's anhydride), n-hich completely siihlimcd on heating. Palmitic Acid and Calcium Chloride. A mixture of palmitic acid and calcium chloride n-as hpated to 170' C. in the above way. T o reniove silver palmitate, n-hich might be formed n-ith silver chloride. the crude silver chloride precipitate was washed with nitric acid. The silver chloride rcmuining n-eighcd 3.4 grams. .Ifter the reaction. calcium chloiidc remaining in thc reaction flask was renioved by thoroughly extracting n-ith nater. The n-ater-insoluble residue was fractionally rrvrystallizcd from ethyl alcohol to give 5.2 grams of less soluble calcium palmitate and 16 grams of the recovered palmitic acid. The calrium palmitate obtained was treated with dilute sulfuric acid to furiiish calcium sulfate. The mixture n-as then estracted with et,her. Evaporation of ether followed by recryst'allization from n-hexane gave palmitic acid, the melting point of which (63" C.) did not depress when the mix melted n-it,h authcnt,ic palmitic acid. Phenol, Calcium Chloride, and Iodine. Phenol and iodine did not give a silver iodide precipitate in t h e silver nitrate t r a p \Then heated as above. A mixture of phenol, calciuni chloride. and iodine (0.1 mole) n-as heated t o 160' C. to yield 3.0 grains of silver chloride n-hich was identified from its color (first white, then t'uriied to dark violet-gray) and it's large solubility in ammonia (completely dissolved). -1lthough iodine was also condensed in t'he silver nitrate trap, the color of the silver chloride precipitate could be observed easily. The reaction products Tvere steam distilled t'o furnish dark brown heavy oil. The oil was decolorized with sodiuni bisulfite, washed with water, dried, and distilled in vacuo. The first run gave a positire Beilstein test' for halogen (iodine). It might consist of a mixture of phenol and o-iodophenol, for both had almost t'he same boiling points. The main fraction, weighing 4.0 grams, was recrystallized from ethyl alcohol and nater to give faint'ly y e l l o ~crystals, t'he nielt,ing point of lyhich (92" C.) did not depress when the mix melted with an authent'ic 4-iodophenol prepared according to the Xeumann method(l3). Resorcinol, Calcium Chloride, and Iodine. Compounds were heated as
above. T h e reaction product in the flask n as extracted 111th benzene, the benzene removed, and the residue was recrystallized from hot n ater t o give 0.2 gram of Stenhause's 4-iodoresorcinol ( I d ) , m.1). 67" C. (impure 4,A-rliiodoresorcinol) ( I S ) , which n a s dissol1 ed in 10% sodium hydroxide and bcnzoylated L))- the Schotten-Bauniann nirthod to > icld 4.6-dibenzoylresorcinol, dtnxnl)ofcd a t 195" to 200" C. (13). Mesitylene, Aluminum Chloride, and Benzoyl Chloride. To a n ice-
moled mixture of 24 grams of mesityl m e a n d 4 grams of benzoyl chloride, 6.1 grams of aluminum chloride n a s nddcd and heated 5 hours a t 120' C . T h e liquid phase changed from colorless t o J ellow, orange, red-brom-n, a n d tlarh brown. .ifter the reaction, 100 grams of ice, 20 ml. of concrntrated hydrochloric acid, and 1.50 nil. of n a t e r n ere added suceessi~(~1y. The oily upper layer was separated, n-ashed TI ith 11 ater, dried over sodium sulfate, and distilld to give 10.5 gram? of rccol wed nicaitylcnc (h.12. 61' C. at 20 mni. of Ffg), 1 .O gram of solid iiiipurc dureiir
(b.1). 85" C. at' 20 mni. of Hg.), 3.2 grams of pale yellow viscous oil (b.13. 85" to 90' C. a t 20 mm. of Hg) (impure isodurene), and 4.8 grams of yellow viscous oil (b.p. 150" to 155" C. a t 5 nim. of Hg.) (impure benzoylmesit,ylene). The durene fract'ion was sublimed a t 40" t'o 50" C. t o give 0.8 gram of durene, colorless, in.p. 80" C., n-ith a camphor-like odor. Mesitylene, Calcium Chloride, and Benzoyl Chloride. A mixture of 2 1
grams of mesitylene, 4 grams of henzoyl chloride, and 25 grams of calcium chloride !%-asheated a t 165' C. for 9.5 hours and the product was n-orked u p as above and distilled t'o gire 13.2 grams of recovercd mesitylene, 0.3 gram of durene, 1.1 grams of impure isodurene, a n d 1.5 gram of impure lienzoylniesit,ylene.
LITERATURE CITED
( 1) "Beilsteiiis
Hundhuch der organisclien Chemie," 4th ed., F-01. VI, p. 208, Springer-Verlag, Berlin, 1923. ( 2 ) "Chemistry of Carbon Compounds," E. H. Rodd, ed., T'ol IA, p. 274, 1951; IIIA, p. 439, Elsevier, S e w York, 1954. (3) Uatta, S . P., J . Indian Chem. Soc. 16, 573 (1939). (4)Elbs, K , > J . p r a h t . U z e m . 35, 186 (1887). ( 5 ) Feinl. F. (Seminar a t T o k o Univer- - 1
--
\ - - - - I
(6) Feigl, F., s t a r k - l I a y r , C;., l'nlanta 1, 252 (1958):
