636
J. Org. Chem., Vol. 40, No. 5, 1975
Wood, McIntosh, and Lau
Formolysis Product Studies. Ditosylate 4 (1.013 g, 0.002 mol) was added to a solution of 0.272 g (0.004mol) of sodium formate in 40 ml of formic acid (freshly distilled from boric anhydride) equilibrated at 40'. After 4.5 hr (5 half-lives) the mixture was cooled to room temperature and diluted with 150 ml of ether. Formic acid was removed by extraction with NaHC03. The ether extract was dried over anhydrous MgS04 and concentrated by distillation. Two components were isolated by preparative vapor phase chromatography (SE-30, 150°, 60 ml/min). The major component was assigned structure 9: nmr (CDC13) 6 0.9 (d, 3), 1.1 (d, 3), 1.5 (m, 8), 2.0 (m, 51, 4.9 (m, l),7.9 (s, 2); ir (neat) 1725 cm-l (ester C=O).8 The minor component was assigned structure 10: nmr (CDCls) 6 0.9 (d, 3), 1.5 (m, 7), 2.0 (m, 7), 5.3 (s, 2), 7.9 (s, 1);ir (neat) 1730 cm-l (ester C=O).6 Product composition was determined by analytical vapor phase chromatography. Thermal conductivity factors were assumed to be identical for each component, and the amount of each product was determined as the percentage of the total area under the trace. Structures 9 and 10 were confirmed by characterization of the products of formolysis followed by saponification with 50 ml of 0.5 M NaOH. Two components were isolated by preparative vapor phase chromatography (Carbowax, 120°, 60 ml/ min). The major component was assigned structure 11: nmr (CDCIB) S 0.8 (d, 3), 1.0 (d, 3), 1.5 (m, ll),2.1 (m, 3), 3.8 (m, l),4.4 (br s, 1);ir (neat) 3500 (0-H), 1710 cm-1 (C=O); mass spectrum (IO eV) m/e 198 (small), 180, 165, 147, 139, 125, 112, 97,83, 69, 67.8 Anal. Calcd for C1ZH2102: C, 72.68; H, 11.18; 0, 16.14. Found: C, 71.51; H, 10.2L15The minor component was assigned structure 12: nmr (CDC13) 6 0.9 (d, 31, 1.5 (m, lo), 2.2 (m, 5), 5.3 (br s, 2); ir (neat) 1710 cm-l (C=O); mass spectrum (10 eV) m/e 180, 165, 139, 125, 112, 97, 83, 70.8 Anal. Calcd for C12H2oO: C, 79.94; H, 11.18; 0, 8.88. Found: C, 78.77; H, 11.09.16Pure samples of 9 and 10 were hydrolyzed independently to products having identical retention times (by peak enhancement) to those of 11 and 12, respectively. The reaction was also stopped after 1 half-life and the resulting mixture was diluted with ether. Formic acid was removed by extraction with NaHCOa. The organics were concentrated by rotary evaporation, and the residue was chromatographed on a silica gel column. Elution was begun with 2% THF-hexane. The products 9 and 10 came off with 10% THF-hexane. One or more mixed formate tosylates came off with 15% THF, and unreacted ditosylate with 20-50% THF. The mixed formate-tosylate fractions were allowed to react with wet formic acid, and the resulting products were 9 and 10. Trifluoroacetolysis Product Studies. Ditosylate 4 (1.012 g, 0.002 mol) was added to a solution of 0.475 g (0.004 mol) of sodium trifluoroacetate in 40 ml of trifluoroacetic acid (1%anhydride) at 25O. After 5 half-lives (determined by changes in the aromatic methyl resonances) the solvolysis was worked up in the manner described for formolysis. Two components were isolated from the
ether extract by preparative vapor phase chromatography (SE-30, 130°, 60 ml/min). The major component was assigned a structure analogous to 9: nmr (CDC13) 6 0.9 (d, 3), 1.1 (d, 31, 1.5 (m, 8), 2.0 (m, 5), 4.9 (m, I); ir (neat) 1780 cm-I (ester C=O).8 The minor component was assigned a structure analogous to 10: nmr (CDC13) 6 0.9 (d, 3), 1.5 (m, 7), 2.1 (m, 7), 5.3 (s, 2); ir (neat) 1800 cm-I (ester C=O).s Pure samples of these products were hydrolyzed to materials with vapor phase chromatographic retention times identical (by peak enhancement) to those of 11 and 12, respectively. Trifluoroacetolysis followed by saponification resulted in materials having nmr and ir spectra identical with those of 11 and 12 produced by formolysis. Registry No.-4, 53013-73-3; 9, 53783-61-2; 9 (trifluoroacetyl analog), 53783-62-3; 10, 53783-63-4; 10 (trifluoroacetyl analog), 53783-64-5; 11, 53783-65-6; 12, 53783-66-7; 5-chloro-l-pentyne, 14267-92-6;acetylene, 74-86-2; l-bromo-3-chloropropane, 109-706; 1,8-dichloro-4-octyne, 53783-67-8; 6-dodecyne-2Jl-dio1, 5378368-9; p - toluenesulfonyl chloride, 98-59-9; sodium trifluaroacetate, 2923-18-4.
References and Notes (a)This work was supported by the donors of the Petroleum Research Fund, administered by the American Chemical Society, and by the National Science Foundation (Grant GP-35888X); (b) National Science Foundation Trainee, 1969-1970; NDEA Fellow, 1970-1973. (2) W. D. Ciossen and S. A. Roman, TetrahedronLett., 6015 (1986). (3) P. E. Peterson and R. J. Kamt, J. Amer. Chem. Soc., Q l 4521 , (1969). (4) H. R. Ward and P. D. Sherman, Jr., J. Amer. Chem. SOC., 89, 1982 (1)
(1987); 90, 3812 (1968). (5) Secondary tosyiates have been found to favor flve-membered ring formatlon.2,3Although the products are therefore deplcted throughout this
paper as five-membered rings, we do not exclude the concomitant presence of some six-membered ring products. (6) The ditosyiate 4 can exist in dl and meso diastereomeric modifications. We are presuming that the Isolated product 18 isomericaiiy pure, but this presumption does not alter our conclusions (see Discussion).We have no way of knowlng which diastereomer is present in our study. (7) J. B. Lambert and A. G. Holcomb, J. Amer. Chem. SOC., 93, 2994 (197 1).
The nmr and Ir spectra are reproduced in J. J. Papay, Ph.D. Dissertation, Northwestern University, 1973. (9) The remainder of the reaction mixture consisted of several minor products, none accounting for more than 5 %. (10) H. Feikin and C. Lion, Chem. Commun,, 60 (1988). (1 1) P. D. Bartiett and G, D. Sargent, J. Amer. Chem. Soc., 87, 1297 (1985). (12) G. D. Sargent and M. J. Harrison, Tetrahedron Lett., 3699 (1970). (13) i. Marszak, J.-P. Guermont, and R. Epsztein, Bull. SOC. Chlm. Ff., 1807 (8)
(1980).
(14) (15)
Patterned after a synthesis of n-butylacetyiene by K. N. Campbell and B. K. Campbell, "Organic Syntheses," Collect. Vol. IV, N. RabJohn,Ed., Wiiey, New York, N.Y., 1943, p 117.
Twice-collected samples stili exhibited some Impurities by vpc. The poor elemental analyses must result from these impurities, which had little or no affect on the nmr, ir, and mass spectra.
Field Desorption Mass Spectrometry of Phosphonium Halides Gordon W. Wood,* John M. McIntosh and Pui-Yan Laul Department of Chemistry, Uniuersity of Windsor, Windsor, Ontario, Canada N9B 3P4 Received September 3, 1974
Field desorption mass spectra are reported for six mono- (1-6) and four bisphosphonium halides (7-10) derived from triphenylphosphine. All of the former show base peaks corresponding to the phosphonium cation and several show other peaks of structural significance. Base peaks for the latter are influenced by structural factors, in particular, the stability of a complex of the dication with one halide. Fragmentation and the general behavior of these compounds under field desorption conditions are discussed in terms of the utility of this technique for confirmation of structure of these important synthetic intermediates. Organic "onium" salts, and phosphonium salts in particular, are increasingly important intermediates for organic synthesk2 T h e increased acidity conferred on protons adjacent to the positive center allows their easy removal and the ylides so formed react in a variety of useful ways, depending largely on the nature of the heteroatom i n ~ o l v e d . ~ While the preparation of such salts is usually straightforward, difficulties can arise. For instance, rearrangement
during quaternization of phosphines with allylic halides4 can lead to unexpected products or mixtures o f products. The use of dihaloalkanes can lead to mixtures of mono- and bisphosphonium salts,5 and salts derived from addition of triphenylphosphine hydrobromide to polyenes or alcoh o l ~can ~ lead ~ , to ~ products with ambiguous structures. During a continuing investigation of the preparation and synthetic application of vinylphosphonium salts,7 such
J. Org. Chem., Vol. 40, No. 5, 1975 637
Field Desorption Mass Spectrometry of Phosphonium Halides problems were encountered and in particular we required a rapid and reliable method for the determination of molecular weights of the products of quaternization of triphenylphosphine. Since electron-impact mass spectrometry is not suitable for such nonvolatile compounds, we turned to the recently developed field desorption technique which has already been applied to ammonium Salks We report here the results obtained from a number of related mono- and bisphosphonium salts of established structure which clearly indicate the utility of field desorption mass spectrometry (FDMS) in structure determination of these compounds. Numerous reviews outlining the principles upon which FDMS depends have appeared since Beckey first demonstrated the technique in 1969, including a recent brief and lucid account of FDMS in the context of field ionization from which it is d e r i ~ e dThe . ~ key facts are that a nonvolatile sample can be deposited on an anode which is subsequently inserted into the mass spectrometer source. Upon application of a high positive voltage (and usually some heat) to the anode, electrons are removed from sample molecules and the resulting low-energy molecular ions are focused and detected in the usual way.
Results and Discussion Phosphonium halides 1-10 (Chart I) yield FD spectra which are highly characteristic of their structure at minimum anode temperatures, along with fragmentation which increases as anode temperature is increased.
Chart I
*
Ph,PCH,Ph
C1-
Ph,PCH,CH,
Br-
(353)
(35, 37)
(291)
(79, 81)
2
1 +
t
Ph,PCH,CH=CH, (303)
Br-
Ph,PCH=CH,
Br'
(79, 81)
(289)
(79, 81)
3
4
+
+
Ph,PCH=C (CH3)z (317)
C1'
Ph,PCH,CH=CHCH,
(35) 37)
(317)
6
5 *
+
Ph,P(CH,),PPh, (552)
C1: (35, 37)
+
Ph,P(CH,),PPh,
2Br(79, 81)
(566)
7
2Br' (79, 81)
8 +
(580)
2Br' (79, 81)
9 +
+
Ph, PCH,CH=CHCH,PPh, (578)
(trans)
1, R = CH,Ph; X
2C 1(35, 37)
10
The presence of two isotopes for each of the halogens (35C1 = 75.4%, 37Cl = 24.6%; 79Br = 50.6%, 81Br = 49.4%) aids in the identification of peaks to which they contribute and in addition a comparison of observed and calculated isotope peak intensities provides an opportunity to check on the reproducibility of minor peaks. The results for monophosphonium halides 1-6 are presented in Table I. The phosphonium cation gave rise to the base peak in each of these spectra. From the point of view of determination of an unknown structure, the fact that there are frequently several peaks of higher m/e may be a nuisance, but the family of ions representing the original cation is so much more intense than any others that a correct assignment should be relatively straightforward. Similar identification of the halide would be possible only for 1, where the
X-a
= C1; anode current = 16 m A
m/e 744 (2.6%), 743 (6.3), 742 (7.9), 741 (14), 674 (5.01, 649 (5.8), 571 (7.1), 495 (10.5), 479 (5.0), 477 (5.5), 443 (6.5), 429 (15), 399 (7.6), 390 (5.5), 389 (121, 388 (14), 387 (34), 355 (7.9), 354 (501, 353 (100, base), 299 (8.1), 298 (9.2), 297 (24), 277 (3,1), 262 (3.4) 2, R = CH,CH,; X = Br; anode current = 13 mA m/e 664 (5.50/0), 663 (13), 662 (6.2), 661 (111, 369 (2.91, 367 (5.6), 343 (4.71, 341 (4.4), 292 (37)) 291 (100, base) 3, R = CH,CH=CH,; X = Br; anode current = 13 mA m/e 688 (3.3%), 687 (5.8), 686 (3.2), 685 (5.6), 381 (2.2)) 343 (3.6), 305 (4.0), 304 (31.5), 303 (100, base), 277 (3.1) 4, R = CH=CH,; X = Br; anode current = 15 mA m/e 660 (5.10/0), 659 (8.3), 658 (4.3), 657 (7.5), 290 (21.7), 289 (100, base) 5, R = CH=C (CH,),; X = C1; anode current = 10.5 mA m/e 319 (80/0), 318 (30), 317 (100, base)* 6, R = CH2CH=CHCH, (trans); X = C1; anode current = 10 mA m/e 319 (5%)) 318 (48)) 317 (100, base)c
QAll ions of relative abundance greater than 5% and others of .particular interest are reported. Cluster ions near 669, 671 are too small to be measured accurately. Cluster ions at 669, 671 are below threshold. One scan at high gain yields 669 = 2.0%, 671 = 0.8%.
peak a t 387 corresponding to the major isotope of chlorine associated with the cation less one H has a relative intensity of 34%. All of these compounds show some evidence for a singly charged cluster ion composed of two cations and one anion (+-+), although 5 and 6 would present some difficulty in anion identification as unknowns. Reference has been made to the fact that the base peak in these spectra occurs as part of a family, and in the case of 1, the peaks assigned to the neutral salt less an electron appear to have a hydrogen missing. This observation of hydrogen gain and loss is very common in FDMS and represents a limitation of this method for structural studies. However, in the present work 'where molecules are composed mainly of atoms of high mass number (P, C1, Br) combined with stable groups (CcHs), hydrogen transfer presents no particular difficulty. It should be noted that molecules containing 20 or more carbons have substantial 13C isotope peaks (20 X 1.1 = 22%), and after subtraction of this contribution, the amount of M H and M 2 H is not very large. However, assignment of fragmentation peaks requires that one or occasionally two hydrogens be treated as disposables to be added or subtracted. This arbitrary procedure may take on some mechanistic meaning as larger numbers of FD spectra on various classes of compounds become available. Benzyltriphenylphosphonium chloride (1) gives a particularly rich FD spectrum, a fact which may be related to the low ionization potential of the benzyl group. In addition to the base peak f m l e 353) and peaks arising from the intact phosphonium halide (mle 387-390), there are several assignments that are straightforward. Triphenylphosphine (mle 262), which could arise from benzyl loss from the base peak, and the elements of methyltriphenylphosphonium cation ( m / e 277) are peaks found in most of our compounds. The peaks a t mle 297, 299 correspond to Ph3PCl+ and show the appropriate isotope ratio. Most of the other peaks can be tentatively assigned by manipulation of the major structural units, although a t this stage the manner in which these sometimes thoroughly rearranged fragments actually arise is not clear. The peaks a t 649, 571, and 495 correspond to loss of PhCH3, PhCH3 C6H6, and PhCH3
+
+
Ph,P(CH,),PPh,
Table I + Field Desorption Mass Spectra of Ph3P-R
+
+
638 J. Org. Chem., Vol. 40, No. 5, 1975
Wood, McIntosh, and Lau
Table I1 + Intensity of Cluster Ions in Ph3P-R Compound
Cluster m/e
Intensity,
a
?4
13
C and + H b
1, R = CH,Ph; 741, 743 14, 6.3 7.9, 2.6 x = c1 2, R = CH2CH3; 661, 663 11, 13 6.2, 5.5 X = Br 3, R = CH,CH=CHz; 685, 687 5.6, 5.8 3.2, 3.3 X = Br 4, R = CH=CHZ; 657, 659 7.5, 8.3 4.3, 5.1 X = Br Relative to base peak = 100. b Intensities for peaks 1amu above those quoted (e.g., 742,744for 1).
+ C6H4 from the major isotope peak of the cluster ion a t mle 741. There are two ions that may be related to additions to the base peak, i.e., mle 429 (353 C6H4) and m/e
+
Table 111 + Field Desorption Mass Spectra of (Ph3P)zR X-a
X-
+
443 (353 PhCH). Addition of C1 to the latter would give mle 478, 480, a process which may be represented by the peaks actually found one unit lower. Whether this exercise in provisional assignment has any merit or not, study of this compound does emphasize that under some conditions FD produces a good deal more than molecular ions. The remaining compounds in Table I give much simpler spectra. There is evidence in 2 for PhSPBr+ (341, 343) as well as small peaks which may represent the phosphonium halide - 3 H (mle 367, 369). For compound 3, the peaks a t 343 and 381 may represent the addition of allyl (actually C3H4) and benzene to the base peak by analogy with the 429 and 443 peaks in 1. However, at this level the absence of isotope peaks may be accidental, and it is therefore possible that these peaks are bromine containing. Attention has already been drawn8 to the existence of ion clusters in FDMS. Our results confirm this behavior, and the presence of isotopes for each of our anions allow these assignments to be made with some confidence. In Table I1 we present the ions corresponding to two phosphonium cations combined with one halide anion for compounds I-
4. The intensities of the cluster ions reflect fairly accurately the isotopic composition of chlorine (1) and bromine (2-4). Although the contribution of extra hydrogens to these peaks could in principle distort the observed ratios, a quick calculation shows that the “l3C and +H” peaks are in fact predominantly composed of l3C, a result of the high carbon number (40-50) of these cluster ions. Thus, these data show that FD ion peaks of 5-15% relative intensity contain sufficient ions that they reproduce fairly faithfully the expected isotope ratios. In fact, our experience has been that reasonable ion statistics and reproducibility are maintained a t even lower intensity levels when measurement of peak intensities is not complicated by noise. The observed FD spectra for bisphosphonium salts 7-10 are presented in Table 111. Unlike the monophosphonium salts, these compounds have base peaks which appear to be related to their specific geometry. Thus, 8 and 9 have (+-+) ions as base peaks, rnle 645,647 for the former, and 659, 661 for the latter. Compound 7 has corresponding peaks (631,633) of low intensity and 10 has peaks one unit higher (614, 616) which we attribute to (+-+) H. It is difficult to escape the conclusion that the unusually prominent cluster ions in 8 and 9 reflect their ability to form a ring-like structure with the halide held between the two phosphorus atoms. Whether the failure of 7 to show this enhanced cluster peak is related to ring-size problems or to competition from favorable fragmentations (both methy-
+
7, R = (CH2)2;X = Br; anode current = 16 mA m/e 659 (5%), 657 (41, 633 (7), 631 (61, 291 (6), 290 (35), 289 (100, base) 8, R = (CH2&;X = Br; anode current = 18 mA m/e 649 (22%), 648 (29), 647 (811, 646 (491, 645 (100, base), 303 (22) 9, R = (CH,),; X = Br; anode current = 17.5 mA m/e 663 (9701, 662 (44), 661 (100, base), 660 (431, 659 (89), 291 (l),290.5 (4), 290 (8)’ 10, R = CH,CH=CHCH2;‘ X = C1; anode current = 15 mA m/e 661 (4%), 660 (11),659 (6), 658 (121, 617 (4) 616 (5), 615 (7), 614 (15), 339 (13), 316 (6), 292 (8), 291 (29), 290.5 (24), 290 (100, base), 276 (7) All ions of relative abundance greater than 5% and others of special interest are reported. 0 At high gain, small peaks are present at 341, 343 (PhaPBr,
