Polarographic Behavior of Organic Compounds. XII. Relative Ease of CarbonHalogen Bond Fission in the Iodobenzoic Acids, Phthalic Anhydrides and Phthalates Rs PHILIPJ. ELVING AND CLIFFORD I,. HILTON RECEIVED SOVEMBER 2(J, 1951 Benzoic acid and phthalic anhydride give no polarographic waves in the pH range of 5.4 to 11.5. I n ammonium chlorideammonium hydroxide buffer stepwise removal of halogen atoms was observed for polyiodophthalic anhydrides. Tetraiodophthalic anhydride yields four waves, triiodophthalic anhydride three waves, each of the four diiodophthalic anhydrides two waves, and 4-iodophthalic anhydride one wave. The reduction in each case corresponds with the fission of one carbonhalogen bond and the replacement of the halogen by hydrogen. I n all other buffers, 3,6-diiodophthalic anhydride gives but one wave and triiodophthalic anhydride two waves; one wave in each case is apparently due to a loss of two halogen atoms. 911 other diiodo derivatives show two waves regardless of buffer or PH. The correlation of reduction potcntial and positiori in the molecule has been indicated for the iodo derivatives of benzoic ant1 phthalic acids.
.Uthough the present work deals largely with tlie The present investigation was directed toward the tietermination of the effect of position on the ring iodobenzoic acids and diiodophthalic anhydrides, upon the ease of carbon-halogen bond fission for several runs were made with 3,4,6-triiodo- and anhydrides. Stepwise revarious iodo derivatives of benzoic and phthalic 3,4,5,G-tetraiodophthalic duction representing fission of carbon-halogen acids. Benzoic acid was reported' to be reducible a t bonds is also found in these aromatic compounds - 1.87 v. us. S.C.E. (saturated calomel electrode) (Table VII). Of the four waves given by tetrain tetrabutylammonium iodide and 50% dioxane. iodophthalic anhydride, the most negative one coIn the present work, using only aqueous media, incides with the third wave of triiodophthalic anno reduction of benzoic was observed either in hydride; the second wave of diiodophthalic anhybuffered solutions (pH 0.6 to 11.5) or in unbuffered dride, and the only wave for monoiodophthalic 0.5 M LiCl solution. Furman and BrickerJ2who anhydride. The third wave of the tetraiodoinvestigated phthalic acid over the PH range of 1 phthalic anhydride corresponds with the second to S, reported that below pH 1.0 the phthalic acid wave of the triiodophthalic anhydride. The nonwave merges with the hydrogen wave, from pH coincidence of the second wave of tetraiodophthalic 1 to 2 one wave due to phthalate is obtained just anhydride with the first wave of triiodophthalic before the hydrogen wave, and above PH 2.0 no anhydride is probably due to errors in measurement waves are obtained unless multivalent cations are of the first wave of the latter compound a t very low prcsent. The present study of phthalic anhydride concentrations. The first wave of the diiodo derivatives depends (pH 0.6 to 11.5)leads to similar conclusions; only in KCl-HC1 buffer a t PH 1.i could any reduction on the position of the iodine atoms on the aromatic be obtained, where two rather indistinct waves were ring. Iotlinc atoms meta to the carbonyl group found. Accordingly, i t appeared likely that any seem to bc more easily reduced than those in the reduction which did occur with the iodobenzoic ortho position. Also, when two iodine atoms are acids and phthalic anhydrides and acids would ortho to each other, the first is more easily removed represent loss of the halogen atom and replaceinent than when they are meta. The tneta configuration, in turn, is more readily attacked than the para. by a hydrogen atom. Two more or less distinct waves were reported The small difference in potential between that for for each of the iodobenzoic acids in 66% ethanol the fission of a carbon-iodine bond in the 3-position and 0.01 AT tetraethylammonium bromide, and in and that for one in the 4-position is understandable buffered solution3; single waves were found4in 20';;: in tcrnis of thc equivalency of the two positions on ?-propanol containing 170tetramethylammoniuiii the basis of analogous cffects on ortho and para locaticms. : I group in the 3-position is ortho and broniide and 2,(557Q, sodium carbonate (pH 1 1 .:i'). Diiodobenzoic acid derivatives gave t vvo wa\-es iii para to the two carboxyl groups while one in the 5 psitioil is p r a and ineta. the latter ,Ilthough thc iodine-carbon-carboxyl arraiigcThe stepwise renioval of halogen atoiiis froin I )trlyhalogenated cotnpouncls has been r e p o r t e d for ments :ire n o t identical, the greater stability of an thc chlorinated niethanesj and halogenated acetic iodine--carbon bond in an aromatic molecule is seen for o-iodobenzoic acid a t acid^.^^^ It was felt that a polarographic study of by comparing the EL/? the polyiodobenzoic and phthalic acid derived t'1\7es 111-1s.s ant1 1 1 3 ( - 1.45 and - I .SSv.j with that (d mould provide data indicating the relative reactivi- iotloacctic acid a t the same PH values (- 0.50 m t l ties of halogen atoms in the various positions on the -0.39 v.). aromatic ring. Experimental (,l) S. Wawzonek, IC. '1. Laitiiien and S . J . K;rviatko\rski. Tuls 66! 887 (1964). I ? ) N li F u r m a n a n d C. I?. Bricker. zbid , 64, ROO ( l ~ l 4 2 1 I:$! t:. G f r f i P I y and '1'. T1erl:tlr. .I ( ' h e l l 2 .so, , 1 x ~ 1 0 . 5 1 , t.L! I< T I h r t o w s . H A Ilcrns arid J LI P d g e , i I,ee, D. Stocrsova and
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