3531 computer program provided a rate constant with standard error based on one standard deviation. In each case, at least six points were used to determine the pseudo-first-order rate constant, and no deviation from the first-order kinetics was observed. Run 54. The general procedure of run 47 was utilized with 149.1 mg of (&)-2-d, 0.3 ml of DBN, and 19.7 ml of tert-butyl alcohol. Run 55. The general procedure of run 39 was followed utilizing 16.6 mg of (+)-2-d, 0.01 5 ml of PMG, and 2 ml of tert-butyl alcohol. The initial observed rotation was a Z 5 o b s d $0.195' and the final was (YZ50bsd +0.071 O at 436 nm. Run 61. To a solution of 110 mg of ( f ) - 2 in 10 ml of tert-butyl alcohol was added 0.04 ml of PMG. The solution was mixed thoroughly and placed in a thermostated bath at 49.8". Aliquots were withdrawn at appropriate times and shaken with 2 N hydrochloric acid, ether, and a trace of methanol. Subsequent procedures followed the pattern of run 47. Run 60. To a solution of 22.1 mg of (+)-2-d in 2 ml of tertbutyl alcohol was added 0.003 ml of PMG. The solution was mixed thoroughly, and a portion was transferred to a 1-dm polarimeter cell which was thermostated by water circulating from a 51.1" bath. The temperature of the water was measured immediately after leaving the polarimeter cell at 50.9". The initial observed rotation was Ly50'g0brd +0.198", and the final observed rotation was a50 ',,bsd +0.029" at 436 nm. Subsequent procedures for recording data and determining base concentration were patterned after run 39. Run 49. The procedure of run 60 was applied to 22.0 mg of (-)-l-d in 2 ml of ter?-butyl alcohol followed by 0.012 ml of PMG. -0.490", and the final The initial observed rotation was a4' observed rotation was a4' 'obsd -0.092" at 436 nm. Kinetic Components of Isotopic Exchange-Racemization Reactions by the Reresolution Technique. Run 66. The procedure as applied to (+)-1-d reactions in methanol-potassium methoxide has been detailed else~here.'~Only an outline is given here. A solu-
tion of 320.1 mg of ( - ) - I d ([a]25546 -32.7' (c 1.3, dioxane), containing 0.96 atom of excess deuterium per molecule) in 25 ml of terf-butyl alcohol was thermostated at 25.0". By a graduated syringe, 0.4 ml of PMG was added and the solution was mixed thoroughly. A portion of the solution was transferred to a thermostated polarimeter cell. When the rotation decreased to -0.292' from an initial rotation of (ILz5abad -0.579' at 546 nm the solution was quenched with hydrochloric acid. Aliquots from the polarimeter cell were titrated with standard hydrochloric acid to a phenolphthalein end point to give a base concentration of 0.105 M . The quenched mixture was extracted with ether. The combined ether solutions were washed with water, dried (Na2S04), and concentrated to 275 mg of a dry, white solid A. An ir spectrum of solid A showed the typical absorption spectrum of 1 and no spurious absorptions. This material was subjected to fractional crystallizations in reagent grade acetone. Rotations were taken in dioxane at 546 nm and 25.0". Recrystallization of solid A gave 50 mg of solid B having [a]25546 +0.53" ( c 1.1, dioxane), mp 132-133" (racemic 1, lit.4b mp 133-134"). From the mother liquors of B, 150 mg of solid C was recovered. Solid C contained two distinct types of crystal structures. These structures were separated manually into prisms D having [(2]25545 - 16.1" ( c 1.12, dioxane) and plates E having [a]25j46 -31.3" (c 1.6, dioxane). Recrystallization of the plates E gave solid F having [a]25j46 -31.4' ( c 1.65, dioxane) ( 9 5 z optically pure), mp 126-128" (optically pure 1, lit.4b mp 127-128", [ a ] 2 5 5 4 5 +33.7", c 1.1, dioxane). Solids B and F contained 0.76 and 0.88 atom of excess deuterium per molecule, respectively, by mass spectrometry using the direct insertion technique. The values of k l , kt, and k s were calculated from the above data with the method detailed p r e v i o u ~ l y ,and ~~ they are recorded in Table VII. Kinetic Runs of Table VI. Runs 62-65 were identical with runs 39, 44, 51, and 55, respectively, except the former runs involved many more data points.
Base-Catalyzed Nucleophilic Substitutions at Pentacoordinated Phosphorus Fausto Ramirez,* Gordon V. Loewengart, Elefteria A. Tsolis, and Koa Tasaka Contribution from the Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11790. Received July 30, 1971 Abstract: The alkoxy groups that occupy the equatorial positions in the trigonal-bipyramidal pentacoordinated phosphorus atom of four-membered cyclic tetraoxyalkylphosphoranes are replaced by the alkoxy groups of alcohols, under base catalysis. Analogous base-catalyzed nucleophilic substitutions are reported for five-membered cyclic unsaturated pentaoxyphosphoranes. The rings are preserved in these substitutions. T h e relative rates of (a) the substitution reactions a n d (b) the permutational isomerizations of the trigonal-bipyramidal oxyphosphoranes determine the course of the substitutions. The reactions of phosphonites, RCH2P(OCH3)2, of phospinites, (RCHJ2P(OCH3), a n d of tertiary phosphines, (RCH2),P, with highly electrophilic carbonyl compounds, e.g., hexafluoroacetone, constitute a general synthesis of 1,2-0xaphosphetanes with pentacoordinated phosphorus.
T
his investigation is concerned with the mechanism of nucleophilic substitutions at the pentacoordinated phosphorus of the 1,2-0xaphosphetane ring system,2 e.g., 1 RVOH + 2 R"'0H; see Chart 1. We are also concerned with substitutions at the pentacoordinated phosphorus of the 1,3,2-dioxaphospholene ring ~ y s t e m e.g., ,~ 3 R"'0H + 4 R"OH; see Chart 11.
+
+
+
+
(1) This research was supported by grants from the National Cancer Institute of the NIH (CA-04769) and from the National Science Foundation (GP-6690). (2) (a) F. Ramirez, C. P. Smith, J . F. Pilot, and A. S. Gulati, J . Urg. Chem., 33, 3787 (1968); (b) F. Ramirez, C . P. Smith, and J. F. Pilot, J . Amer. Chem. SOC.,90, 6726 (1968). (3) F. Ramirez, K . Tasaka, N. B. Desai, and C. P. Smith, ibid., 90, 751 (1968).
The four-membered cyclic oxyphosphoranes required in this research have four or three oxygen atoms attached to the phosphorus, 1, 2, or 5, respectively. Previous work from this laboratory2 has shown that the reaction of tertiary phosphines, e.g., 6 (Chart 111), with hexafluoroacetone (7) gives derivatives of the 1,3,2-dioxaphospholane ring system, 8 (Chart IV), w h i c h can be transformed into oxaphosphetanes w i t h t w o oxygen atoms attached to the phosphorus, 9 (Chart I). The overall reaction 6 7 -.t 8 -+ 9 proceeds in excellent - yields, and the dioxyphosphetanes 9 are remarkably stable. The cyclic intermediates in the usual variation of the Wittig olefin synthesis4 are
+
(4) (a) G.Wittig and U. Schollkopff, Chem. Ber., 87, 1318 (1954);
Ramirez, Loewengart, Tsolis, Tasaka
Substitutions a t Pentacoordinated Phosphorus
3532 Chart I
Iy
No. X 1 R”’0 2 R”’0 5 R”’0 9
Y
R
R’
R”’0
H H H CH, H H CHI
H H H H H H H H H H H H H H
RVO RCHi
C*H,
CH,O C,H,
H
R“ H
H H CF3 H CF.
Chart I1
R‘
z No. 3 4 31 32
X
Y
Z
R
R‘
R”O R”O
R“0 R”’0
R”O R”O
CHaO CeHr CHzO CeH5CHzO CH3O
CHaO CHvO
H H CH3 CH3
H H CHa CH3
CH3
CH3
CH3
CH3
CHsO CHIO C&5CHzO CeH5CHzO
33 34
CeH5CHzO CeHr CHzO
phosphetanes 9 require relatively drastic conditions for their transformation into olefin, R R ’C=C(R”)2, and phosphinate, 11, (XYZ)PO. The dioxaphospholenes 3 and 4 required in this study have been described, and the problems associated with the permutational isomerizations of the oxyphosphoranes, in general, have been considered in detail elsewhere.6-8 Results Reaction of Phosphonites and Phosphinites with Hexafluoroacetone. Dimethyl methylphosphonite (12) and dimethyl ethylphosphonite (13) (Chart 111) react with hexafluoroacetone (7) at -70” to give mainly derivatives of the 1,3,2-dioxaphospholane ring system 14 and 15 (Chart IV). Small amounts (15 % or less) of the 1,2oxaphosphetanes 16 and 17 (Chart I) are also formed in these reactions. The oxaphosphetanes 16 and 17 produced in the low-temperature reactions of the trivalent phosphorus compounds with the ketone do not result from further transformations of the dioxaphospholanes 14 and 15, as can be demonstrated in independent experiments. However, the pyrolyses of the phospholanes 14 and 15 at much higher temperatures, ca. 120-140”, also produce the phosphetanes 16 and 17. To support the structure assigned to the oxaphospholanes 14 and 15, the reaction of dimethyl phenylphosphonite (18) with hexafluoroacetone (7) was also
ur; ”
0
18
7
Chart 111
I9 RCHaP
M
No.
Y ‘
X
Y
R
X
Y
R
13 20 Chart IV
No.
investigated. Now, the resulting phospholane 19 lacks the hydrogen atoms in the equatorial ligand that are required for the ring contraction to the phosphetane. The data given in the Experimental Section support structure 19. The reaction of methyl diethylphosphinite (20) (Chart 111) with hexafluoroacetone at -70’ gives ca. 85% of phospholane (21) (Chart IV), and 15% of a mixture of stereoisomeric phosphetanes 22 and 23 (Chart I). When this reaction is carried out at 20”, the products are the phospholane 21 and the phosphetanes 22 and 23 in ca. 42, 26, and 22%, respectively. The phosphetanes must have been formed from precursors of the phospholane, since the latter, 21, is trans23, quite slowly even at formed into the former, 22 much higher temperatures (ca. 100’). The stereoisomeric phosphetanes 22 and 23 are not interconverted at about 100’. A relatively slow stereomutation 22 23 is observable at ca. 120-140” in the
+
*
phosphetanes with only one oxygen atom attached to phosphorus, e.g., 10 (Chart I), and are quite unstable. This difference is the result of the marked decrease in the stability of oxyphosphoranes as the number of highly electronegative ligands decreases. While the , ~ dioxyWittig intermediates 10 are seldom i ~ o l a b l e the (b) S. Trippett, Quart. Reu., Chem. Soc., 17,406 (1963); (c) A. W. Johnson, “Ylid Chemistry,” Academic Press, New York, N. Y., 1966. (5) (a) G. H. Birum and C. N. Matthews, Chem. Commun., 137
(1967); (b) G. Markl, Angew. Chem., In!. Ed. Engl., 4, 1023 (1965);
(c) F. G. Mann, “The Heterocyclic Derivatives of Phosphorus, Arsenic, Antimony and Bismuth,” Wiley-Interscience, New York, N. Y., 1970. (6) Possible mechanisms for these and related permutational isomerizations of the trigonal bipyramids will be discussed in subsequent communications. The literature on this subject was reviewed recently; see ref 7 and 8. (7) F. Ramirez, BulL S O C .Chim. Fr., 3491 (1970). (8) F. Ramirez, I. Ugi, S. Pfohl, E. A. Tsolis, J. F. Pilot, C. P. Smith, D. Marquarding, P. Gillespie, and P. Hoffmann, Phosphorus, 1, 1 (1971); (b) I. Ugi, D. Marquarding, H.Klusacek, P. Gillespie, and F. Ramirez, Accounts Chem. Res., 4, 288 (1971).
Journal of the American Chemical Society / 94:lO / M a y 17,1972
3533
presence of the acid hexafluoroisopropyl alcohol. In contrast, the stereomutation 24 a 25 of the dioxyphosphetanes is relatively fast at 100” in the presence of hexafluoroisopropyl alcohol. The isomerization occurs by a bond rupture-recombination mechanism,sa and the reluctance of the trioxyphosphetanes 22 and 23 to undergo the permutational isomerization is consistent with their enhanced stability due to the three highly electronegative oxygen ligands. The trigonal-bipyramidal structure for the cyclic oxyphosphoranes, with the rings in the apicoequatorial skeletal position, is based on the results of X-ray analy ~ i s . ~ ~The ~ O placement of the alkyl and aryl groups in the equatorial position follows from the lower electronegativity of the carbon atom relative to oxygen. 1 , 1 2 The ‘H nmr spectra of the phospholanes 14 and 15 in solution at 30” show one signal due to the two CH3O groups. If these phospholanes were “frozen” in the time scale of nmr, one should observe two C H 3 0signals, barring accidental degeneracy, since the C H 3 0 groups are magnetically nonequivalent.6 The ‘H nmr spectra of the oxaphosphetanes 16 and 17 in solution at 30” show, respectively, one C H 3 0 signal and two C H 3 0 signals. Now, the “frozen” phosphetane 16 has two magnetically equivalent C H 3 0 groups, while the “frozen” phosphetane 17 has two magnetically nonequivalent C H 3 0 groups. Moreover, as discussed elsewhere,‘+* if these phosphetanes 16 and 17 undergo relatively rapid positional exchange of the ligands at 30”, the two C H 3 0 groups of 16 should give one ‘H signal, while the two C H 3 0 groups of 17 should still give two ‘H signals. The 19Fnmr spectrum of the phospholane 21 (Chart IV) in solution at 30” shows only one fluorine signaL6 The “frozen” structure 21 should give rise to two fluorine signals since in it there are two sets of magnetically nonequivalent CF3 groups. Base-Catalyzed Substitutions in 1,2-Oxaphosphetanes. The phosphetane 16 does not react with methanol under the conditions specified in the Experimental Section. The addition of acid does not promote the reaction; however, the addition of catalytic amounts of triethylamine results in the substitution of the hexafluoroisopropoxy group by the methoxy group to give a trimethoxyoxaphosphetane (30, cf. Scheme I). The course of the substitution can be followed by ‘H nmr spectroscopy in CDC1, as solvent and with CDBODand pyridine as reagents; the results are shown in Figure 1. The key observation is that C H 3 0 D appears ca. 30 sec after the addition of 1 molar equiv of C D 3 0 D to thephosphetane 16. The amount of CH,OD increases in the early stages of the reaction and then decreases (note the signal at the highest magnetic field in curves 11 through VI11 of Figure 1). As the reaction proceeds, the amount of (CF3),CHOD increases as this
Figure 1. Pyridine-catalyzed reaction of 2,2-dimethoxy-2hexafluoroisopropoxy - 4,4 - bis(trifluoromethy1) - 2,2 dihydro 1,2oxaphosphetane (16) with 1 molar equiv of C D 3 0 D in CDC13 solution at 25”: (I) ’H nmr spectrum, no CD,OD added; (11-VIII) 1 molar equiv of CDIOD added; (IX) 0.5 molar equiv of CHaOH added to product of spectrum VIII. Times after addition of CDaOD: (11) 2 min 30 sec; (111) 8 min 30 sec; (IV) 14 min; (V) 22 min 30 sec; (VI) 35 min 30 sec; (VII) 43 min; (VIII) 59 min. Each spectrum = 50 sec. The doublet of solid curve in 11-VI11 is due to (CH30)2[(CH3)2CHO]P< and (CH30)(CD,0)[(CF8)2CHO]PP(OR)(OR'z), and >P(OR'), were available from previous work. The relative amounts of the four dioxaphospholenes present in a given reaction mixture were determined from the integration of the 1H nmr signals of their R O and R'O groups and of their CH3C=CCH3 groups. The amounts of alcohol, ROH, produced were followed in the same manner. The results are given in Tables I and 11. p-Toluenesulfonic acid had no noticeable effect on the substitution reaction of 31.
+
z
-+
+
-.f
Reactions of the Tri-p-anisylmethyl Carbonium Ion with Nucleophiles' C. A. Bunton* and S. K. Huang Contribution from the Department of Chemistry, University of California, Santa Barbara, California 93106. Received July 29, 1971 Abstract: Kinetic salt effects upon the forward and back reaction of the tri-g-anisylmethyl carbonium ion with water have been measured. These salt effects and those upon the activity coefficient of the alcohol allow us to determine the relative stabilities of the hydronium and carbonium ions and the transition state, Xi. The salt order upon fH +ifR+ is LiC104 NaC104 > NaBr > NaNO, > NaCl > LiCl > no salt CsCl > Me4NC1 KC1; upon f H - / f x * it is LiC104 NaC104> NaBr > NaN03 > NaCl Me4NC1 CsCl no salt > LiCl KC1; and upon f~+/fx=kit is Me4NC1> no salt CsCl > NaCl > KC1 > NaBr NaN03 > LiCl > NaC104 > LiC104. These relative activity coefficients are considered in terms of direct and indirect interactions between the salts and the reacting species. The second-order rate constant for reaction of the carbonium and hydroxide ions is 8200 1. mol-' sec-l, and the kinetic salt order is no salt > Me4NC1> KC1 NaCl > NaBr > NaN0, > NaC104> LiCl > LiC104. The second-order rate constant for attack of azide ion is 5 x lo6 1. mol-' sec-1, and the first-order rate constant for ionization of the alkyl azide is 75 sec-l at 25.0' in water.
--
-
N
-
N
--
-
N
N
T
he stability of carbonium ions in aqueous solution is of considerable importance. Stable triarylmethyl carbonium ions, e.g., Malachite Green and Crystal Violet, react relatively slowly with anionic and other nucleophile^,^^^ but attack of water on the triphenylmethyl carbonium ion in acetonitrile is modsec), and erately fast on the nmr time scale4 (7 = allylic carbonium ions have half-lives of < 10-5 sec, in hydroxylic so1vents.j Taft and his coworkers found that the reactivity of triarylmethyl carbonium ions (1) Support of this work by the National Science Foundation is gratefully acknowledged. (2) (a) E. F. J. Duynstee and E . Grunwald, J. Amer. Chem. SOC.,81, 4542 (1959); (b) J. Dixon and T. C. Bruice, ibid., 93, 3248 (1971). (3) C. D. Ritchie, G. A . Skinner, and V. G. Badding, ibid., 89, 2063 (1967). (4) J. I. Brauman and W. C. Archie, ibid., 92, 5981 (1970). (5) D. S . Noyce and S. I
