Detection of Unsubstituted Para Position in Phenols SAUL SOLOWAY and ANGEL0 SANTORO' Department of Chemistry, The City College, College of the City o f New York, New York,
Phenols are readily oxidized to colored products in ammoniacal solution by persulfate ion in the presence of a catalytic amount of silver ion. Derivatives having a free para position are distinguished from others in yielding blue or green dyes, which are pH as well as redox indicators. Evidence is given for the belief that these dyes are derivatives of indophenol. The nature of the catalysis by silver ion and the anomalous behavior of a few phenols are discussed.
not contain strong electronegative groups such as nitro, cyano, carbonyl, amide and carbalkoxy, gave a blue or green color on oxidation with persulfate in ammoniacal solution containing silver ion. Other derivatives were either unoxidized or gave yellow or amber colors. Table I lists the results. In order to obtain a positive result (blue or green color) with phenols containing electronegative substituents in ortho or meta positions, the compound was first boiled with zinc dust and alkali. This treatment either hydrolyzed or reduced these groups to electropositive ones which. if anything, enhanced the oxidation with persulfate.
A
DILUTE ammoniacal solution of phenol when oxidized by persulfate, hypochlorite, or hypobromite ions in the presence of a catalytic amount of silver ion was found by Escai'ch ( 1 ) to yield a green or blue solution. The chemistry and the scope of this reaction have never been investigated, I n a review article on qualitative tests for the phenolic group Gibbs ( 2 ) suggested that the color developed in the Escaich reaction was due to the oxidation of phenol by silver ammonium ion. The implication of this suggestion is that persulfate ion functions as the oxidant to maintain the concentration of the silver ammonium ion. A test of this hypothesis showed that Tollens reagent (silver ammonium ion) in quantity was incapable of producing the Escaich color reaction. However, the addition of argentic oxide to an ammoniacal solution of phenol gave a green color. Since , argentic oxide is prepared O by the oxidation of argentous ion with alkaline persulfate, the nature of the silver ion catalysis in the Escaich reaction is clear. The structures of the green and blue compounds formed in this oxidation have not been elucidated. Gibbs ( 2 ) demonstrated that 2,6-dibromo-N-chloroquinoneimine condenses with a phenol having an open para position to produce the corresponding dibromoindophenol derivative. Singer and Stern ( 4 ) used the Gibbs teat as the basis of a quantitative spectrophotometric determination of Reveral phenols. Since phenol, ammonia, and an oxidant, the essential components of the EscaIch reaction, could produce an intermediate a t the same oxidation level as A;-chloroquinone imine, the indophenol may possibly be the blue component produced in the reaction. Experiments showed that of the many amines tested ammonia was specific for green or blue color formation. The colors produced with phenol in the reaction corresponded with the known colors of indophenol in both acid and alkali solutions. Further, the color could be bleached by reduction with zinc dust and reformed by autoxidation. This latter behavior is characteristic of indophenol dyes. A comparison of the absorption spectra of several reaction mixtures with that of a known solution of indophenol showed many similarities. However, they were far from identical, and the spectra of the reaction mixtures changed considerably with time. This observation was undoubtedly due to the fact that the colored intermediates were subjected to further oxidation with persulfate. Several attempts were made a t isolating and purifying the dye components by conventional methods. After several variations a chromatographic method yielded a solution which matched the spectrum of indophenol fairly well as shown in Figure 1. However, the amount of material recovered from the separation waa too small to substantiate its identity by the preparation of derivatives. The tests of 65 phenols showed that, with a few exceptions, only those derivatives which had unsubstituted para positions and did 1 Present address, Department of Chemistry, University of Kansas, Lawrence, Kan.
N. Y.
*0350
450
550
650
750
650
950
Millimicrons
Figure 1. Absorption spectra 1. Indophenol (purchased) in presence of potassium persulfate 2. Ether extract of chromatographed material
A notable exception to the observation that a free para position was necessary for a positive test was the case of some para halogenated phenols. Qualitative tests showed the absence of chloride or oxidized ions of chlorine in these experiments. If it is aesumed that the similar colors obtahed were also the result of the formation of para indophenol derivatives, it follows that the halogen group migrated to another position on the ring. EXPERIMENTAL
The addition of a few milligrams of solid potassium persulfate to an aqueous ammoniacal solution containing a catalytic amount of silver nitrate gave an excellent test with phenol and some of its low molecular weight derivatives, which were sufficiently soluble in the medium. However, with m-pentadecylphenol, the hydroxybiphenyls, and the hydroxystilbenes, it was necessary to add some aqueous alkdli and/or pyridine to increase the solubility. During the tests of a number of phenols, observations were that salicylanlide, salicylonitrile, salicylate esters, o-hydroxyacetophenone, etc., gave yellow colors like the para substituted phenols. If these compounds were treated with zinc dust in alkaline solution prior to oxidation, thev acted as typical phenols with free para positions. The following procedure was therefore used to detect an unsubstituted para position in phenols. Ten to 20 mg. of a phenol was dissolved in 1 ml. of 221 aqueous sodium hydroxide. If the compound was not totally'soluble, 2 or 3 drops of pyridine were added. Then 50 mg. of zinc dust was also added and the solution was refluxed for a maximum of 5 minutes. After centrifugation and decantation of the supernatant liquid, 2 ml. of concentrated ammonia, 2 drops of 231 silver nitrate, and 10 to 20 mg. of potas-
798
V O L U M E 2 7 , NO. 5, M A Y 1 9 5 5
799
sium persulfate were added. Within 5 to 15 seconds a green, blue-green, or blue solution resulted for compounds containing open para positions. Otherwise, yellow, orange, or amber colors resulted. Regardless of the color the resulting solution was heated with 30 mg. of zinc dust Centrifugation showed the supernatant liquid had become much lighter if not colorless. Decantation, followed by shaking with air, caused reoxidation to the previous color. I n some cases a few drops of 3% hydrogen peroxide mere added to accelerate the oxidation. Several attempts were made a t isolating the blue compound produced in the oxidation of 50-gram batches of phenol by the method described. I n these experiments the phenol solution was not pretreated with zinc dust. The oxidation was carried out at 0" C. because the blue color was more stable a t that temperature toward excess persulfate ion After standing for about 1 hour the reaction mivture was poured i&o excess dilute hydrochloric acid and extracted nith chloroform. The addition of ligroin to the chloroform eytract caused a relatively small amount of a dark amorphous solid to precipitate. This material melted with decomposition a t 85 to 90 C. Recrystallization from some common solvents proved ineffective in purifying this material. After several unsuccessful variations the following chromatographic procedure yielded a solution which gave an absorption spectrum almost identical with that of a known sample of indophenol A column of Merck's 100-mesh alumina, 10 inches high, was prepared by filling the absorption tube with ligroin (60" to 90" C. boiling range) follon-ed by the addition of alumina in small amounts with vigorous shaking. After the alumina had settled, the ligroin was allowed to drain out until its surface coincided with that of the adsorbent. The sodium salt of the extract was dissolved in 0 5 ml. of absolute methanol and added to the column. The dye was strongly adsorbed at the top of the column. The column was then washed down with ligroin saturated with absolute methanol. While much of the material remained a t the top of the column, some moved down to form another zone This second zone \vas SeDarated from the rest of the alumina column and extracted wit6 ether. The ether was removed in vacuo, the residue diqwlved in n-nter, and the absorption measured as rapidly a s pqssihle with a Model B Beckman spectrophotometer. Figure sholvs a comparison of the ppectrum of this solution ith that of a knoii n solution of sodium indophenolate.
,~
Table I. .4. Phenols with Free P a r a Positions" 1 . Acetylsalicylic acid 2. m-Bromophenol 3. o-Bromonhenol Butvl salicylate 6-Ciiloro-2-methv!~~henol m-Chlorophenol a-Chloronhenol I. 8 . m-Cresol I). o-Cresol 10. 2,4-Dihydroxybenzoir acid b 11. m-Ethylphenol 12. a-Hydroxyacetanilide C 13. o-Hvdroxvacetonhenonn 14. 2-H$drox$-4-aininobrnzoic acid 15. m-Hydroxybenzaldehyde 16. m-Hydroxybenzoic acidd 17. o-Hydrosybenzyl alcohol 18. a-Hydroxybinhmvl 19. 2-Hydroxy-3-methouybenzal dehj:de 20. 1 -Hydroxy-2-naphtiioic acid 21. o-Iodophenol 2 2 . .Vono-fVerf-bii tvl-nr-vesol 23. o-Sonvlnhenol " 24. m-Pentadecylphenol 2 5 . Phenol 26. P h e n r l sllicylate 27. 8-Qiiinolinol 28. Resorcinol monoacetate 29. Salicylamide 30. Salicylic acid 31. Sslicylonitrile 3 2 . Thymol 33. 2,6-Xylenol
B. Phenols with Substituted Para Positions 34. 35. 36. 37.
38.
39. 40. 41.
42. 43.
Benzyl p-hydroxvbenzoate p-Bensylphenol p-Rromorihenol 2-C hloro-5-hydroxytoluene p-C1,lorophenol 4-Chloro-Z-phen ylphenol
2-C hloro-4-phenylphrnol 5-Chlorosalicylic acid 6-Chlorot hvmol p-Cresol
Results of Color Tests
Color before and after Reoxidation of Leuco Dye Light green Deer, green Deen blue Deep green Deep blue Deep green Deep blue Deep green Deep blue Deep blue-green Deep green Deep green Light green Oranee Deedgreen Deep green Deep blue-green Deep green D-ep green Light green Deep green Deep green Deep green Deep green Deep blue-green Deep green Deep orange Crern precipitate Light green Deep green Light green Deep green Deep blne
Orange Orange-yellow Light green Deep green Light green Deep green Uellou.
Orange-yellow Orange-yellow Light yellow
RESLLTS 4 \ D DISCUSSION
The data of Table I show that for most of the derivatives tested, those with vacant positions para to the phenolic group gave green or blue colors. Certain anomalies, horT ever, did manifest themselves. The orange color obtained in the case of Z-hydroxy4-aminobenzoic acid is probably due to simultaneous oxidation of the amino group with the consequent formation of a competing chromophore. 8-Quinolinol also gave an orange color, typical of many phenols with electronegative groups. Unlike the nitro or carbonyl groupp, u hich are readily reduced by zinc dust in alkaline solution, the pyridine ring in this case remains intact. The observation of color formation in two stages proved repetitious in most cases, but was helpful in the case of 2,4-dihydrouybenzoic acid The latter gave an orange-red color in the first stage and a blue-green in the second This behavior may be due to the presence of another oxidizable group such that the reaction proceeds beyond the indophenol stage in the presence of persulfate. Houever, reduction n ith zinc dust followed by autoxidation caused the leuco base to go back to the indophenol stage only. A second addition of persulfate caused the reformation of the orange-red color observed in the first stage. The nature of the reaction of ammoniacal persulfate on para substituted phenols was not investigated. It is unlikely that the para substituted products were oxidized to o-indophenols to any Although the literature on these derivatives ia Scarce and many Proposed structures are not based on d i d evidence, Hodgson and Sicholson @) definitely prepared 3,3' difluoro-o-indopheno~by the action of acid on m-fluorophellol. This compound is red in a h l i n e solution and can be reduced to the leuco form n i t h zinc dust and acetic acid, which in turrlis autoxidizable. silllilar colors and behavior were llot observed with the oxidization producb obtained from the para substituted phenols.
B.
Phenols with Substitnted P a r a Positions
Color before and after Reoxidation of Leuco Dye
p-(a-Cumyl) phenol 45. trans-ar,a'-Diethylstilbestrol 46. 4,4'-Dihydroxydinhenyl 47. 4,4'-Dihydroxydiphenyl sulfone 48. 2,6-Dirnethyl-4-bromophenol 49. 3,5-Dimethyl-4-chlorophenol 50. Ethyl p-hydroxybenzoate 21. hleso-hexestrol 0 2 . p-Hydrouyacetanilidieb 53. p-Hydroxyacetophenone 54. p-Hydroxybenzoic acid 55. p-Hydroxybenzophenone 26. p-Hydroxydiphenyl 37. 3-Hvdroxy-2-naphtlioic acid 58. p-Hydroxypropiophenone 5 9 . Methyl p-hydroxybenzoate 60. 5-Phenylsalicylic acid fil. n-Propyl p-hydroxybenzoate 62. 2-Quinolinol 63. Sulfosalicylic acid 64. 2,4,6-Tribromophenol 6 5 . 2,4,6-Trichlorophenol
Yellow-brown precipitate Deep yellow Brown-orange Deep orange Yellow Deep yellow Orange Deep yellow Orange-yellow Orange-yellow Yelloworange Yellow Orange-yellow Light yellow Light yellow Yellow Orange Orange-yellow Light yellow Orange Deep yellow Deep yellow
44.
a Deriratires possessing hydroxy or aiiiino groups ortho or para t o a given hydroxy group reduced t,he silver aintnoniuin ion t o metallic silver. T h e compounds themselves were rai3irlly oxidized to quinhydrones, quinonee,
quinone imines, etc., which in turn iinderpo roniplex condensations in alkaline solution. Hence, in most of these ca.3e.F.gray or b r o v n solutions containing siiniiarly colored precipitates resulted by the action of alkaline persulfate. Although o-nitronhenol gave a dark green color in the test, other nitro denvstives such as 2-nitroreuorcinol, X,5-dinitrosalicyiic acid, and m-nitrophenol caiised the reduction of silver aniirioniiiiii ion and brown colorations. b After t h e oxidation of this comrloiind a i t l i persulfate the color is a n orange-red instead of the usnal blue or green. However. after the solution is reduced with einc dust and rroxidized by air. it becomes blue-green. c 0 - and p-Hydroxyacetanilides pave tlie typical colorations of their respective groups,if they were not preheated with zinc in boiling alkali. Apparently, the oxidation proceeds rapidly in conipariPon with the hydrolysis of the acetyl gror!p so t h a t the latter remains intact. If these derivatives are first refluxed witb zinc and alkali, the resiilting solutions, consisting of the free 0 - and p-aniinophenols, reduce silver animonium ion. d m-Hydrosybenzoic acid showed behavior opposite to 2,4-dihydroxybenzoic acid. On oxidation with niersiilfate the solution was green, b u t after rrduction with zinc dust followed b y autoyidation the solution becan!e orange. T h e first stage color obtained in the oxidation of this compound 1s greatly improved when the reaction is carried out around O o C .
ANALYTICAL CHEMISTRY
800 The anomalous behavior of the para halosubstituted phenol? requires further study. To make certain that the results observed were not due to impurities, many of these derivatives were recrystallized as many as six times from different solvents. The colors obtained from the most purified fractions showed no qualitative differences from the original samples. It ma!- be concluded from the ten para halogenated phenols tried that if both the positions, ortho tJo either the halogen or phenol groups, are subst,ituted, the compounds behaved like other phenols with blocked pai'a positions. Other instances point up the importance of the 2-chloro-5-hydroxytoluene gave a nature of the group-e.g.. positive test and 5-chlorosalicglic acid a negative one. Zincke and coworkers ( 5 ) observed the migration of groups in the oxidative nitration of certain para substituted phenols. For example. 4-methyl-6-chlorophenol was oxidized with nitric acid to 2-nit,ro-4-chlorotoluquinone and,'or 2-chloro-4-nitrotoluquinone. This work strengthens the hypothesis that the para haiogen atom in certain phenols may migrate under oxidative conditions. 4either chloride ion nor osidized ions of chlorine could he detected after the persulfate oxidation. Escaych's observat,ion t'hat hypobromite or h!.pochlorite ions can be substituted for persulfate ion wa8 confirmed. S-Bromosuccinimide, S-chlorosuccinimide, and 1.3-dichioro-5,5-dimethylhydantoin are also usable and may offer some advantage if the test, is to be carried out in a nonaqueous solution. The solubilities of inorganic persulfates are extremely low i n these media. Sodium peroside, potassium chlorate, potassium iodate.
and potassium bromate are ineffective substitutes for potaspimi persulfate. Many of the common metallic ions capable of existing iii more than one valence state were tried i n lieu of siiver ion as catalysts. Cupric ion seemed to be the only effective substitute. Thoriuni(IY), cerium(IV), praseodymiuni(II1 i. and neodymium(II1) were of doubtful value. The sensitivity of the test varied considerably with the conipound. .Ilthough phenol could readil?. he detected in a 0.03% aqueous solution, the concentration of salicjdic acid had to be increased tenfold before an adequate color, resulted. By studJ-ing details of the reaction environment surh as temperature, and conceut,rations of the reactants. the .sensitivity may be grentlv increased. Finally. the test was found to he of w l u e in detecting persiilfute ion in the presence of other oxidants incapohle of giving the Eecai'ch reaction. LITERATURE CITEI)
Ebcaich. d.,J . pharnt. d i m . , 22, 140 (19200,. Gihbs, H. D., Chem. Reus., 3, 291 (1927). Hodgson. H. H.. a n d Kicholsoii. D . E.. J . ('hem. Soc., 1939, gp. 1405-8. J., a n d Stern. E. It.. A s ~ r . CHEY.. . 23, 1511 (1951). (4) Singer, ( 5 ) Zincke. T.. a n d coworker-. Ani?.. 328, 314 (1903); 341, :313 (1905).
Colorimetric Determination of Sulfate Ion JACK L. LAMBERT, STANLEY K. YASUDA, and MORRIS P. GROTHEER Department o f Chemistry, Kansas State College, Manhattan, Kan.
4 colorimetric procedure for determining sulfate ion in the range of 0 to 400 p.p.m. is described which uses an insoluble thorium borate--4maranth d>e reagent. Sulfate ion releases dFe molecules from the solid reagent in direct proportion to its concentration and is determined indirect15 as the concentration of the dye at 521 niM. Potentiall) serious interferences b? fluoride, phosphate, and bicarbonate ions are eliminated through the use of added lanthanum ion and a weak acid cation exchange resin. Seven water samples were analFzed by this method with the results in good agreement with standard gravimetric analysis.
T
HE determination of fluoride ion by the cellulose-supported thori~m-~4maranth lake ( 1 ) suggested that a similar method could be used for the determination of sulfate ion. The reagent used is thorium borate treated with Amaranth dye, which releases dve niolecules in proportion to the sulfate ion concentration in solution. Bicarbonate, phosphate, and fluoride ions interfere by reacting with the thorium-dye reagent to release dye into solution. Phosphate ion interferes a t concentrations not ordinarily found in water. The addition of lanthanum ion removes the fluoride ion with little effect on the sulfate ion. Bicarbonate ion interferes. but is eliminated b>- passing the sample solution through iimberlite IRC-5O(H) weak acid ion exchange resin. \Gth the use of lanthanum ion and a cation exchange resin. sulfate ion exchanges stoichiometrically for the dye molecules with the thorium-dye reagent with no interference from other ions. REAGENTS
an^ E Q U I P M E ~ T
Thorium borate-Amaranth reagent, ground to pass 200 mesh. 0.724 gram of potassium Standard sulfate solution, 400 p p m., sulfate per liter of solution.
Lanthanum ion. I000 u.n.ni.. 0.TXu a n i of lanthanum 1iitr:itcA hesahydrate per 250 nil.'df solution. " Weak acid ion exchange resin. hmberlite IRC-SO(H), anal!-ticaI grade Filter paper, Whatman S o . 12 and 50. Funnels Teft tubes. 25 X 200 mm. Interval timer. Spectrophotometer, Beckman llodel DI-, 10-nim. cells. 1Ieasuring spoon made from nickel double-end spatula having a diameter of 0.5 cm. (see Figure 1). PREP4RiTIOV O F RE4GENT
Thorium borate is obtained by the reaction of a 1-liter solution of 0,0131 thorium nitrate and 0.0531 sodium tetraborate, the latter being added dropwise with constant stirring. The thorium borate precipitates as a somewhat gelatinous white solid and settles to the bottom in several minutes. The solution is decanted and the precipitate is centrifuged to remove additional water. With the precipitate equally divided into two 250-ml. centrifuge cups, each portion is washed and centrifuged four times with 100 ml. of water. T o each cup, 100 ml. of 0.2% Amaranth solution are added and shaken for 1 minute to allow thorough mising. The excess dye is centrifuged off, and the solid washed five times with 100-ml. portions of water. After the third n-ashing, the solution is colorless. Water adhering to the precipitate iF removed by washing three times with 100 ml. of acetone. Drying is accomplished by heating the precipitate in the oven a t 60" C. for 30 minutes, after which the precipitate is allowed t o dry a t room temperature for 2 hours. The dried product, which is deep red in color, is ground and sieved, and that which passes through a 200-mesh sieve is collected. The finely divided solid reagent is thoroughly mised. PROCEDURE
The sample is run through the column of ion exchange resin, Aniberlite IRCdO(H), 26 cm. high in a 50-ml. buret. The resin is held firmly in place h y borosilicate glass wool plugs, one being
