The intermediacy of metathiophosphonate PhPSO in the reaction of N-tert-butyl-P-phenylphosphonamidothioic acid with alcohols

Article abstract of DOI:10.1021/jo0483769

(Chemical Equation Presented) Kinetic studies of the reaction of N-tert-butyl-P-phenylphosphonamidothioic acid (1) with alcohols were carried out in CH₂Cl₂ by means of ³¹P NMR spectrometry. The reaction is of the first order with respect to thio acid 1. The first-order rate constant at 30°C increases with increasing methanol concentration below 0.25 M, but otherwise the rate constants are either independent of alcohol concentration (MeOH above 0.25 M, BuOH) or decrease with increasing alcohol concentration (i-PrOH, t-BuOH). The effect of alcohols on the order of the reaction and parameters of activation, as well as results of competition experiments, lead us to the conclusion that reaction of 1 with alcohols occurs by an elimination-addition mechanism involving the association of the thio acid 1 and the alcohol and then formation in the rate-determining step of an encounter complex 2″ involving metathiophosphonate 4, amine, and alcohol. Metathiophosphonate 4 reacts preferentially with the alcohol as the encounter complex (primary alcohols) or after diffusion apart as a free intermediate (hindered alcohols).

Full text of DOI:10.1021/jo0483769

The Intermediacy of Metathiophosphonate PhPSO in the Reaction
of N-tert-Butyl-P-phenylphosphonamidothioic Acid with Alcohols
Tomasz Nonas and Stefan Jankowski*
Institute of Organic Chemistry, Technical University of Lodz, Zeromskiego 116, 90-924 Lodz, Poland
jankowsk@p.lodz.pl
Received September 14, 2004
Kinetic studies of the reaction of N-tert-butyl-P-phenylphosphonamidothioic acid (1) with alcohols
were carried out in CH2Cl2 by means of 31P NMR spectrometry. The reaction is of the first order
with respect to thio acid 1. The first-order rate constant at 30 °C increases with increasing methanol
concentration below 0.25 M, but otherwise the rate constants are either independent of alcohol
concentration (MeOH above 0.25 M, BuOH) or decrease with increasing alcohol concentration (i-
PrOH, t-BuOH). The effect of alcohols on the order of the reaction and parameters of activation, as
well as results of competition experiments, lead us to the conclusion that reaction of 1 with alcohols
occurs by an elimination-addition mechanism involving the association of the thio acid 1 and the
alcohol and then formation in the rate-determining step of an encounter complex 2′′ involving
metathiophosphonate 4, amine, and alcohol. Metathiophosphonate 4 reacts preferentially with the
alcohol as the encounter complex (primary alcohols) or after diffusion apart as a “free” intermediate
(hindered alcohols).
1. Introduction
with t-BuOH is then readily explicable as a consequence
of equal attack on the two faces of the planar metaphos-
phate.4 In principle nonstereospecificity could also be
observed if deprotonation of the immediate precursor of
the product (RO+H-PO32-) is slow enough to allow
alcohol exchange, i.e., displacement of the initial alcohol
molecule by another molecule of alcohol.5
N-tert-Butyl-P-phenylphosphonamidothioic acid (1) has
been used in stereochemical studies to probe the possible
involvement of the metathiophosphonate PhPSO in the
reaction with alcohols.6 Enantiopure 1 was found to react
completely nonstereospecifically with t-BuOH in CH2Cl2
(0.2 M) and largely nonstereospecifically with the more
nucleophilic (less hindered) i-PrOH, but with MeOH the
product was formed with one enantiomer in large excess.
With i-PrOH and MeOH the reactions became more
stereospecific at higher concentrations and nonstereospe-
Stereochemical studies have played a very important
part in clarifying the mechanism of nucleophilic substitu-
tion at four-coordinate phosphoryl and thiophosphoryl
centers. Inversion of configuration has been observed for
the usual bimolecular SN2(P) pathway and nonstereo-
specificity for reactions that proceed by an elimination-
addition mechanism involving a planar three-coordinate
P(V) intermediate.1,2 Tertiary alcohols are resistant to
bimolecular phosphorylation and the phosphorylation of
t-BuOH has been considered a test for the involvement
of a reactive, sterically accessible monomeric metaphos-
phate intermediate.3 The formation of racemic product
in reactions of chiral (16O, 17O, 18O-labeled) precursors
* Corresponding author. Phone: +48-42-631-3152. Fax: +48-42-
636-5530.
(1) Westheimer, F. H. Chem. Rev. 1981, 81, 313.
(2) Hengge, A. C. Transfer of the Phosphoryl Group. In Compre-
hensive Biological Catalysis: A Mechanistic Reference; Sinnot, M., Ed.;
Academic Press: San Diego, CA, 1998; Vol. 1, p 517.
(3) Ramirez, F.; Marecek, J. F.; Yemul, S. S. J. Am. Chem. Soc. 1982,
104, 1345.
(4) Friedman, J.; Freeman, S.; Knowles, J. R. J. Am. Chem. Soc.
1988, 110, 1268.
(5) Herschlag, D.; Jencks, W. P. J. Am. Chem. Soc. 1986, 108, 7938.
(6) Harger, M. J. P.; Pater, C. Chem. Commun. 1999, 931.
10.1021/jo0483769 CCC: $30.25 © 2005 American Chemical Society
Published on Web 12/17/2004
562
J. Org. Chem. 2005, 70, 562-566

N-tert-Butyl-P-phenylphosphonamidothioic Acid Reactions
SCHEME 1
cific at lower concentrations. Those obervations can
be rationalized in terms of two competing pathways:
stereospecifc SN2(P) and nonstereospecific elimination-
addition (EA), the former bimolecular process being
favored relative to the latter by more nucleophilic (less
hindered) alcohols and higher concentrations of alco-
hols.6-10 There is, however a third possibility: a preas-
sociative pathway.11 If the metathiophosphonate inter-
mediate is not sufficiently long-lived to allow diffusion
away from the leaving group (t-BuNH2) it will merely
recombine with the leaving group unless the nucleophile
(ROH) is already in place. The preassociation process can
be stepwise or concerted with a loose SN2-like transition
state, and proceed with inversion of configuration at
phosphorus.
substrate was determined by eq 1:
Nitrogen and hydrogen kinetic isotope effects for the
reaction of 1 with alcohols are slightly sensitive to steric
hindrance of alcohol, as expected for an elimination-
addition process. This conclusion was supported by
results of semiempirical calculations on the PM3 level.
However, for the reaction with methanol the addition-
elimination mechanism cannot be excluded.12
We have now undertaken kinetic studies intended to
establish more definitively the mechanism(s) by which
1 reacts with alcohols, in particular to establish whether
there is any reason to invoke a new pathway, in addition
to stereospecific SN2(P) and completely nonstereospecific
EA. If there is, we would hope to be able to ascertain its
stereochemistry.
δ - δsalt
δacid - δsalt
xacid
)
(1)
where δ is the observed chemical shift of the substrate,
δacid the chemical shift of pure acid 1, and δsalt the
chemical shift of the tert-butylammonium salt 3. For
calculation of the first-order rate constants the observed
substrate concentration was corrected by multiplication
by xacid. The reaction of 1 with alcohols followed first-
order kinetics for at least 2-3 half-lives. In all cases
the rate constants were found to be independent of
the thio acid 1 concentration. For the reaction with
methanol the rate constant is not affected by the alco-
hol concentration above 0.25 M and the average rate
constant is then equal to (7.83 ( 0.23) × 10-4 s-1 at 30
°C (Figure 1).
At lower concentrations of methanol (0.05-0.25 M), the
rate constant increases with increasing alcohol concen-
tration. The average rate constant for reaction with
BuOH is equal to (3.20 ( 0.20) × 10-4 s-1 at 30 °C over
the whole concentration range of 0.05-0.75 M. In the
case of the sterically hindered alcohols i-PrOH and
t-BuOH, the reaction is not much slower but the rate
constants do decrease slightly with increasing alcohol
concentration. At lower concentrations of methanol (0.05-
0.25 M) (Figure 1) the observed first-order constant was
found to increase with increasing the alcohol concentra-
tion. This can be explained by the possibility that reaction
with methanol follows two different pathways simulta-
neously, the first-order EA process and the second-order
AE mechanism, according to eq 2:
2. Results and Discussion
In alcohol-free conditions the fragmentation of 1 leads
to a complex mixture of several products. The 31P NMR
spectrum recorded after completion of the reaction con-
tains 13 signals of similar intensities (δP 67.3, 66.5, 66.1,
64.5, 63.5, 63.0, 62.0, 61.6, 61.5, 61.1, 59.7, 56.2, 54.3).
Decomposition of 1 follows the first-order kinetics with
rate constant of (8.08 ( 0.38) × 10-4 s-1 in dichlo-
romethane at 32 °C. In the presence of alcohols only the
formation of esters 66,13-15 was observed, except that with
tert-butyl alcohol traces of pyrothiophosphonate were
detected in the 31P NMR spectra, as reported previously
(Scheme 1).6
In the course of reaction the 31P NMR chemical shifts
of the substrate 1 (and the product 6) were changing
because of the interaction of the liberated amine with
the acidic substrate (and product). The acid 1 and its
amine salt 3 were observed in the 31P NMR spectrum
as one signal due to fast chemical exchange. The posi-
tion of the 31P NMR signal is a measure of this equilib-
rium. The molar fraction of the acidic form 1 of the
dcP
-
) 1kcP + 2kcP[ROH] ) 1kexpcP
(2)
dt
From the linear plot of 1kexp against methanol concentra-
tion both rate constants were estimated: 1k ) 4.1 × 10-4
s-1 and 2k ) 1.4 × 10-3mol L-1 s-1. However, this concept
does not explain the steady first-order constants above
0.25 M of methanol.
The lack of a strong steric effect of the alcohol is
consistent with little if any involvement of a sterically
sensitive bimolecular SN2(P) reaction with bulky alcohols.
In the reaction of 1 with methanol and other alcohols
first-order plots were observed at all concentrations of
alcohol. In the EA mechanism the rate constant k of the
rate-limiting amine departure step (Scheme 1) should not
(7) Quin, L. D.; Jankowski, S. J. Org. Chem. 1994, 59, 4402.
(8) Quin, L. D.; Hermann, P.; Jankowski, S. J. Org. Chem. 1996,
61, 3944.
(9) Jankowski, S.; Quin, L. D.; Paneth, P.; O’Leary, M. H. J. Am.
Chem. Soc. 1994, 116, 11675. Jankowski, S.; Quin, L. D.; Paneth, P.;
O’Leary, M. H. J. Organomet. Chem. 1997, 529, 23.
(10) Harger, M. J. P. Chem. Commun. 2004, 1952.
(11) Jencks, W. P. Acc. Chem. Res. 1980, 13, 161. Jencks, W. P.
Chem. Soc. Rev. 1981, 345.
(12) Jankowski, S.; Mazur, A.; Nonas, T.; Vokal, B. J. Organomet.
Chem. 2004, in press.
(13) Harger, M. J. P. J. Chem. Soc., Perkin Trans. 2. 1978, 326.
(14) Evdakov, V. P.; Alipova, E. I. J. Gen. Chem. USSR (Engl.
Trans.) 1967, 37, 2573.
(15) Mikołajczyk, M. Pol. J. Chem. 1979, 53, 317.
J. Org. Chem, Vol. 70, No. 2, 2005 563

Nonas and Jankowski
If the equilibrium constant K is much less than unity
(K , 1)7,19 the concentration of the dipolar species 2′ is
given by eq 3:
Kassoc × K[ROH]cP
1 + Kassoc[ROH]
[2′] )
(3)
where cP is the corrected substrate concentration (ob-
served concentration multiplied by xacid).
The steady-state approximation for the complex 2′′ and
the metathiophosphonate 4 concentration gives the equa-
tion for the rate of reaction (eq 4):
dcP
dt
d[6]
dt
-
)
)
k1(k2[ROH] + k3) × Kassoc × K[ROH]cP
(k-1 + k2[ROH] + k3)(1 + Kassoc[ROH])
(4)
When Kassoc[ROH] , 1, the second-order kinetics
should be observed. If the association complex is stable
enough and Kassoc[ROH] . 1, the first-order kinetics
describe the reaction (eq 5):
FIGURE 1. Kinetics of the reaction of 1 with alcohols in
dichloromethane at 30 °C.
dcP
dt
k1(k2[ROH] + k3)
d[6]
dt
SCHEME 2
-
)
)
× K × cP )
(k-1 + k2[ROH] + k3)
kexpcP (5)
If the formation of 2′′ is the rate-determining step and
the encounter complex 2′′ transforms to product faster
than it reverts to zwitterion 2′ (k2[ROH] + k3 . k-1), kexp
) k1 × K. It must be emphasized here that although the
association constant (Kassoc) is not present in the rate
equation, the association with the alcohol should affect
the concentration of dipolar species 2′. This assumption
was deduced from the observation that the experimental
rate constants increase with increase of alcohol hydrogen-
bond donation, measured by the Kamlet-Taft parameter
R: MeOH, 0.93; BuOH, 0.79; i-PrOH, 0.76; and t-BuOH,
0.68.20
The parameters of activation are in accord with the
proposed mechanism. The free energy of activation is
almost independent of the alcohol structure and concen-
tration (Table 1). For the primary alcohols (MeOH and
BuOH) the calculated enthalpies of activation are the
same and the entropy of activation is only slightly more
negative for BuOH. For the bulky alcohols (i-PrOH and
t-BuOH) the enthalpies of activation are significantly
higher and the entropies of activation are less negative,
compared with the unhindered alcohols. This is probably
due to stronger interaction of unhindered alcohols with
zwitterion 2. Primary alcohols are more intimately
involved in reaction (more negative entropies of activa-
tion) and provide more assistance (smaller enthalpies of
activation).
depend on the alcohol structure but the alcohol may
influence the proton transfer in the preequilibrium step,
altering the equilibrium constant K. Thus, the changes
of the experimental rate constants kexp reflect the changes
of the equilibrium constant K. A possible modification of
the mechanism presented as Scheme 1 is the association
of the acid 1 and the alcohol. It consists of the association
process, equilibrium between hydrogen-bonded neutral
form 1′ and dipolar species 2′, and formation of the
metathiophosphonate 4 within the encounter complex 2′′
or as a “free” intermediate (Scheme 2). A cyclic six-
membered intermediate (comparable with 2′) was first
proposed over 45 years ago for hydrolysis of phosphona-
midates.16 Recently a computational study of the hy-
drolysis of the methyl phosphate anion evidenced the
dissociative mechanism also including a six-centered
water-assisted transition state.17,18
To answer the question of the role of alcohol solvation
we have performed competition experiments with both
(18) Bianciott, M.; Berthelat, J.-C.; Vigroux, A. J. Am. Chem. Soc.
2002, 124, 7573.
(19) Benkovic, S. J.; Sampson, E. J. J. Am. Chem. Soc. 1967, 89,
4714. Benkovic, S. J.; Sampson, E. J. J. Am. Chem. Soc. 1971, 93, 4009.
(20) Kamlet, M. J.; Abboud, J. L. M.; Abraham, M. H.; Taft, R. W.
J. Org. Chem. 1983, 48, 2877.
(16) Chanley, J. D.; Frageson, E. J. Am. Chem. Soc. 1958, 80, 2686.
(17) Hu, C.-H.; Brinck, T. J. Phys. Chem. A 1999, 103, 5379.
564 J. Org. Chem., Vol. 70, No. 2, 2005

N-tert-Butyl-P-phenylphosphonamidothioic Acid Reactions
TABLE 1. Activation Parameters of the Reaction of 1 with Alcohols ROH in Dichloromethane
alcohol
concn, M
Ea,
kJ/mol
∆Hq
,
∆Sq
,
∆Gq
,
303
303
kJ/mol
303
J/(mol K)
R
ln A, s-1
kJ/mol
Me
0.15
0.50
0.15
0.50
0.15
0.50
0.15
0.50
22.0 ( 3.6
21.93 ( 0.99
21.67 ( 0.43
21.4 ( 1.5
23.6 ( 1.2
23.4 ( 1.2
25.6 ( 1.2
25.2 ( 1.0
73.8 ( 3.4
73.4 ( 2.5
74.9 ( 1.1
74.1 ( 3.9
81.1 ( 3.1
81.4 ( 3.2
86.8 ( 3.2
86.7 ( 2.7
71.3
70.9
72.4
71.6
78.6
78.9
84.3
84.4
-70.6
-71.0
-73.1
-75.8
-56.9
-56.9
-40.6
-43.5
92.6
92.4
94.6
94.6
95.8
96.1
96.6
97.5
Bu
Pri
But
TABLE 2. Kinetics of the Competitive Reaction of 1
TABLE 4. The Enantiomeric Excess (ee) of 6 Formed in
the Reaction of Enantiopure 1 (0.05 M) with Alcohols in
Dichloromethane at 30 °C
with MeOH and t-BuOH in Dichloromethane at 32 °C
concn, M
alcohol concn, M
BuOH
ee, %
1
MeOH
t-BuOH
104k, s-1
MeOH
1.0
t-BuOH
6a
6b
6d
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.05
0.75
0.95
0.90
0.70
0.50
0.30
0.10
0.025
-
9.60 ( 0.18
6.84 ( 0.28
5.76 ( 0.16
5.82 ( 0.20
5.46 ( 0.15
2.692 ( 0.074
1.113 ( 0.049
0.541 ( 0.016
0.05
0.10
0.30
0.50
0.70
0.90
0.975
88
1.0
0.5
81
72
0.5
81
a
0.7
0.5
0.3
0.1
0.3
0.5
0.7
0.9
1.0
0.7
0.7
85
82
83
82
-
a
-
13
6
6
TABLE 3. The Calculated Ratios kMeOH/kt-BuOH for
Competitive Reaction of 1 with MeOH and t-BuOH
3
0.3
76
9
a Not detectable by 31P NMR.
initial concn, M
product ratio
a
MeOH
t-BuOH
6a/6d
kMeOH/kt-BuOH
0.10
0.15
0.20
0.25
0.90
0.85
0.80
0.75
76/24
76/24
83/17
92/8
36
37
41
37
other than steric factors should be considered to explain
this very high value of the calculated rate constant ratio
(kMeOH/kt-BuOH) in reaction of 4 with alcohols. If the
metathiophosphonate 4 had a finite existence under the
experimental conditions and the alcohols could compete
equally, the ratio kMeOH/kt-BuOH would be expected to be
much lower than observed. However, if the MeOH and
t-BuOH concentrations are different in the solvation
sphere relative to the bulk solution and MeOH wins the
a For details of calculations see the Experimental Section.
MeOH and t-BuOH present in the solution in different
ratios (Table 2).
The presence of t-BuOH in place of MeOH causes
retardation of the reaction, although the product of
reaction with t-BuOH was observed in 31P NMR spectra
only when the fraction of t-BuOH in the alcohol mixture
was 0.75 and higher (Table 3). The decrease of the rate
of reaction without formation of 6d must originate from
the decrease of the concentration of reactive form 2′ in
the presence of t-BuOH. Detection of both products 6a
and 6d at high enough concentrations of t-BuOH allowed
the estimation of the ratio kMeOH/kt-BuOH for the reaction
of metathiophosphonate 4 with MeOH and t-BuOH
(Table 3). This ratio was found to be unexpectedly high
and equal to about 40.
competition, the calculated values of the ratio kMeOH
/
kt-BuOH will not properly reflect the reactivity of the
metathiophosphonate toward the two alcohols. Besides
the preferential solvation the high proportion of MeOH
product 6a may originate from the direct displacement
of amine moiety by methanol (less likely for tert-butyl
alcohol) in stereospecific reaction (k2) with an encounter
complex 2′′.
We have examined the enantiomeric excess of products
6 in the reaction of enantiopure acid 1 with MeOH,
BuOH, and t-BuOH (Table 4). The reactions were carried
out under the same conditions as the kinetic experiments
and the results are complementary to those reported
previously.6 The reaction with BuOH (not previously
examined) is less stereospecific than that with methanol,
but more stereospecificic than that with tert-butyl alcohol
(Table 4).
The addition of t-BuOH practically does not affect the
enantiomeric excess of esters 6a and 6b. With the ROH-
t-BuOH mixture in a 3:7 ratio, ee of tert-butyl ester 6d
was found to be 13% in the presence of methanol and
9% in the presence of butanol, while the reaction with
t-BuOH without any other alcohol present was almost
completely nonstereospecific (ee 3%) as in the previous
report.6 If observed differences are significant, it may
suggest that not only another molecule of methanol but
Previous competition experiments with metathiophos-
phate EtO-POS in reaction with ethanol and tert-butyl
alcohol gave the ratio kEtOH/kt-BuOH equal to 2.1.21 Reac-
tion of methanol and tert-butyl alcohol with PhPO2,
generated thermally from phenyl-2,3-oxaphosphabicyclo-
[2.2.2]octene, yields the ratio kMeOH/kt-BuOH ) 1.8.22
-
Generated from phosphate or phosphonate, anion PO3
reacts in dichloromethane solution faster with methanol
than with t-BuOH by the factor of 3-7.23 Thus, influences
(21) Jankowski, S.; Quin, L. D. J. Am. Chem. Soc. 1991, 113, 7011.
(22) Jankowski, S.; Cieplucha, A. Work in progress.
(23) Ramirez, F.; Marecek, J. F.; Yemul, S. S. Tetrahedron Lett.
1982, 23, 1515.
J. Org. Chem, Vol. 70, No. 2, 2005 565

Nonas and Jankowski
tube containing 0.7 mL of the solution containing 1 and the
alcohol, and was used as a standard. The NMR tube was sealed
under argon. The rate of disappearance of substrate was
determined by diminution of its 31P NMR signal compared to
the standard, when only 31P NMR signals for the substrate,
product, and standard were detected. The actual substrate
concentration was taken as the product of starting material
signal integration (a result of acid-tert-butylammonium salt
equilibrium) and the molar fraction of substrate in the acidic
form in the acid-salt mixture. The 31P NMR spectra were
recorded at 67.6-s intervals (usually 30-50) for kinetics
conducted in the spectrometer. In water-bath experiments the
spectra were measured at various time intervals (no less than
10 spectra) after removal and cooling of the tube.
even t-BuOH can react (k2) with an ancounter complex
2′′ formed by methanol.
The conclusion from the present work on reaction of 1
with alcohols is that stereochemical and kinetic results
are in agreement if the elimination-addition mechanism
with alcohol assistance is invoked. The reactive form of
thio acid 1 is the zwitterion 2′ associated with an alcohol
molecule that converts to an encounter complex 2′′ in the
rate-determining step. From this complex metathiophos-
phonate 4 can be liberated as a “free” intermediate in
the presence of sterically hindered alcohols or can react
with primary alcohols within the complex.
Calculations of the rate constants and Arrhenius parameters
were carried out by the least-squares method. All data are
given with standard deviations. The enthalpy and entropy of
activation were calculated for 30 °C according to Eyring theory.
The ratio of reaction rate constants for methyl and tert-butyl
alcohols with metathiophosphonate 4 was determined by 31P
NMR, for reactions 46-56% complete, based on the following
equation:
3. Experimental Section
3.1. General. 31P NMR spectra were recorded at 101.20
MHz with 85% H3PO4 as external standard. Downfield shifts
are positive.
3.2. Synthesis of N-tert-Butyl-P-phenylphosphonami-
dothioic Acid (1). Both racemic and enantiopure acid 1 were
obtained by a previously published procedure.6,13 The acid was
generated from its tert-butylammonium salt immediately
before use. The measurement of the 31P NMR chemical shift
was carried out in CDCl3 solution at -30 °C to avoid decom-
position (δP 66.4). The chemical shift of the tert-butylammo-
nium salt of 1 was 50.7 ppm.6
3.3. Solvents for Kinetic Measurements. In all cases a
mixture of CH2Cl2/CD2Cl2 (5:1) was used as solvent. The
mixture was dried by fractional distillation over P2O5. The
alcohols used in the reactions were dried by distillation over
magnesium (methyl alcohol) or over calcium hydride (isopro-
pyl, butyl, and tert-butyl alcohols).
3.4. Kinetic Measurements. Reactions were carried out
in NMR tubes, either in the spectrometer or in a water bath,
at constant (within (0.1 °C) temperature. The temperature
of a sample in the spectrometer was calibrated based on a
glycol NMR thermometer.24 A sealed 1-mm glass capillary
containing a 0.05 M solution of triphenylphosphine oxide in
CH2Cl2/CD2Cl2 (9:1) was coaxially placed in the 5-mm NMR
kMeOH
IMeOH
Ct-BuOH
)
×
CMeOH
kt-BuOH It-BuOH
where kMeOH/kt-BuOH is the ratio of reaction rate constants for
methyl and tert-butyl alcohols; IMeOH and It-BuOH are integra-
tions of product signals with methyl and tert-butyl alcohols;
and CMeOH and Ct-BuOH are mean concentrations of alcohols
during the reaction.
Acknowledgment. We are indebted to Dr. Martin
J. P. Harger for numerous helpful discussions during
manuscript preparation. This work was supported by
grant 4T09A 117 24 from the State Committee for
Scientific Research (KBN, Poland).
Supporting Information Available: Full list of rate
constants for the reaction of N-tert-butyl-P-phenylphosphon-
amidothioic acid (1) with alcohols (MeOH, BuOH, i-PrOH,
t-BuOH) in dichloromethane. This material is available free
of charge via the Internet at http://pubs.acs.org.
(24) Ralford, D. S.; Fisk, C. L.; Becker, E. D. Anal. Chem. 1979, 51,
2050.
JO0483769
566 J. Org. Chem., Vol. 70, No. 2, 2005