Crystal Structure of Burgess Inner Salts and their Hydrolyzed Ammonium Sulfaminates

Article abstract of DOI:10.1071/CH19338

The solid-state structures of the Burgess reagent, and its analogous ethyl ester reveal structures indicative of triethylamine solvated sulfonyl imides rather than the more commonly depicted triethylammonium sulfonyl amidate. The existence of a reversibly formed hydrate of Burgess reagent is not supported by present studies, but rather a hydrosylate that does not revert to the Burgess reagent with gentle warming under vacuum was isolated and characterised. Structures of the hydrosylates from both the methyl- and ethyl-amidate esters were determined from X-ray crystallographic analysis and are reported. The crystal structures of the Burgess inner salts exhibit geometries at the sulfur atoms that are intermediate between a planar O₂S=NCO₂R unit and tetrahedral 4-coordinate sulfur centres that would be expected from a strong single (dative) bond between the triethylamine nitrogen and sulfur. The hydrolysed ammonium sulfaminates are water soluble intermolecular salts composed of triethylammonium ions, Et₃NH⁺, and N-(alkoxycarbonyl)sulfaminate, O(^-)SO₂NHCO₂R {R = CH₃ or C₂H₅}.

Full text of DOI:10.1071/CH19338

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2019, 72, 867–873
Full Paper
https://doi.org/10.1071/CH19338
Crystal Structure of Burgess Inner Salts and their
Hydrolyzed Ammonium Sulfaminates*
A C
,
B
A
Anthony J. Arduengo III,
Monica Vasiliu
Yosuke Uchiyama, David A. Dixon, and
A
A
Department of Chemistry and Biochemistry, The University of Alabama, Tuscaloosa,
AL 35487-0336, USA.
B
Department of Chemistry, School of Science, Kitasato University, 1-15-1 Kitasato,
Minami-ku, Sagamihara, Kanagawa, 252-0373, Japan.
C
Corresponding author. Email: aj@ajarduengo.net
The solid-state structures of the Burgess reagent, and its analogous ethyl ester reveal structures indicative of triethylamine
solvated sulfonyl imides rather than the more commonly depicted triethylammonium sulfonyl amidate. The existence of a
reversibly formed hydrate of Burgess reagent is not supported by present studies, but rather a hydrosylate that does not
revert to the Burgess reagent with gentle warming under vacuum was isolated and characterised. Structures of the
hydrosylates from both the methyl- and ethyl-amidate esters were determined from X-ray crystallographic analysis and
are reported. The crystal structures of the Burgess inner salts exhibit geometries at the sulfur atoms that are intermediate
between a planar O2S=NCO2R unit and tetrahedral 4-coordinate sulfur centres that would be expected from a strong
single (dative) bond between the triethylamine nitrogen and sulfur. The hydrolysed ammonium sulfaminates are
water soluble intermolecular salts composed of triethylammonium ions, Et3NHþ, and N-(alkoxycarbonyl)sulfaminate,
O(ꢀ)SO2NHCO2R {R ¼ CH3 or C2H5}.
Manuscript received: 21 July 2019.
Manuscript accepted: 29 July 2019.
Published online: 23 August 2019.
Introduction
Results and Discussion
The Burgess reagent[1–4] has been utilised by synthetic chemists
as a powerful and flexible reagent to dehydrate secondary and
tertiary alcohols,[5] amides,[6] and nitroalkanes,[7] and form
amines[2] (via carbamates) from primary alcohols. The reagent
has found further utility in sulfonations,[1] heterocycle forma-
tion,[8,9] and most recently oxidation reactions.[10] In spite of
these diverse applications, no solid state structure of the Burgess
reagent (either as its commercially available methyl carbamate
ester 1, nor its ethyl ester 2, the ‘inner salt,’ originally prepared
by Atkins and Burgess) has been reported. In the years shortly
before his passing (June 2018), Burgess related to one of us
(AJA) that this popular reagent reversibly forms a hydrate with
water that reverts to the parent powerful dehydrating agent with
only mild warming under vacuum. Indeed, Atkins’ dissertation
contains a claim to exactly this point.[11] However, contrary to
Burgess’s recollection shared with AJA, an X-ray structure on
this putative hydrate was never completed.[12] Given the
strength of the Burgess reagent as a dehydrating agent, even
under mild conditions, the reversible formation of a hydrate is a
puzzling and interesting possibility. Hence, we decided to
explore this aspect of the chemistry of the Burgess reagent in
more detail.
Burgess reagents, the inner salt methyl (1) and ethyl (2) esters,
were prepared by the reaction of the corresponding alkox-
ycarbonylsulfamoyl chloride 3a,b with 2 equivalents of
triethylamine in benzene (Scheme 1).[2]
The solid-state structure of the Burgess reagent was deter-
mined by single crystal X-ray diffraction. The structures of both
the methyl and ethyl carbamate esters were obtained using
crystals formed from tetrahydrofuran solutions. The structures
of the Burgess reagent reveals a long N(triethylamine)y
˚
S(sulfaminate) interatomic distance of 1.90 A. This S–NEt3
distance is surprisingly long and is intermediate between the
dative bond in the trimethylamine–SO2 adduct (2.048 A)[13] and
˚
that found in the trimethylamine–SO3 adduct (1.844 A).[14] Such
˚
2 Et3N
benzene, rt
O
O
+
Et3N
O
O
O
O
S
S
– Et3NHCl
N
OR
N
OR
–
Cl
3a: R = CH3, b: R = C2H5
Scheme 1. Synthesis of Burgess reagents.
H
1: R = CH3, 2: R = C2H5
*In memory of Edward M. Burgess, 1934–2018, scientist, mentor, and friend.
Journal compilation Ó CSIRO 2019
www.publish.csiro.au/journals/ajc

868
A. J. Arduengo III et al.
Table 1. Indicators of sulfur pyramidalization in 1, 2, 3b, 4, 5, 6, and 7
Compound
S-Basal plane distanceA [pm]
Sbasal angles [deg.]
1
Et3N-S(O2)=NC(O)OCH3
Et3N-S(O2)=NC(O)OC2H5
Cl–S(O2)NHC(O)OC2H5
Et3NHþ ꢀO3SNC(O)OCH3
Et3NHþ ꢀO3SNC(O)OC2H5
C7H13N-S(O2)=NC6F5
32.53(10)
31.95(10)
39.78(10)
54.90(9)
54.03(10)
29.04
345.66(5)
346.07(7)
338.58(8)
322.34(5)
322.26(5)
348.35
2
3b
4
5
6
7
C5H10(CH3)N-S(O2)=NCN
31.56
346.35
AThe basal substituents at sulfur are the three attached atoms whose least-squares plane is closest to the sulfur centre, leaving the apical substituent to be the
tertiary amine nitrogens in 1, 2, 6, and 7, the chlorine in 3b, and the most heavily H-bonded oxygens in 4 and 5.
O
O
O
O
F5
CN
S
S
N
N
N
N
O2
C1
O3
6
7
S1
O1
N1
Chart 1.
O4
N2
O2
C1
O3
S1
N1
O4
O1
Fig. 2. Crystal structure of Burgess inner salt ethyl ester 2 (ORTEP
˚
drawings 50 % probability); selected bond lengths (A), S(1)–N(1)
N2
1.5421(19), S(1)–N(2) 1.9040(19), S(1)–O(3) 1.4305(19), S(1)–O(4)
1.4301(18), N(1)–C(1) 1.387(3), C(1)–O(1) 1.205(2), C(1)–O(2) 1.344(2),
and angles (deg.), O(3)–S(1)–O(4) 118.19(12), O(3)–S(1)–N(1) 118.15(12),
O(3)–S(1)–N(2) 101.23(10), O(4)–S(1)–N(1) 109.73(11), O(4)–S(1)–N(2)
100.37(10), N(1)–S(1)–N(2) 106.28(10), C(1)–N(1)–S(1) 121.60(17),
O(1)–C(1)–O(2) 122.9(2), O(1)–C(1)–N(1) 129.8(2), O(2)–C(1)–N(1)
107.23(19).
Fig. 1. Crystal structure of Burgess inner salt methyl ester 1 (ORTEP
˚
drawings 50 % probability); selected bond lengths (A), S(1)–N(1)
1.5471(10), S(1)–N(2) 1.9011(10), S(1)–O(3) 1.4337(9), S(1)–O(4)
1.4344(9), N(1)–C(1) 1.3808(14), C(1)–O(1) 1.2083(14), C(1)–O(2)
1.3501(14), and angles (deg.), O(3)–S(1)–O(4) 117.49(6), O(3)–S(1)–N(1)
118.78(5), O(3)–S(1)–N(2) 102.07(5), O(4)–S(1)–N(1) 109.39(6),
O(4)–S(1)–N(2) 101.56(5), N(1)–S(1)–N(2) 104.79(5), C(1)–N(1)–S(1)
121.97(8), O(1)–C(1)–O(2) 122.78(10), O(1)–C(1)–N(1) 130.12(11),
O(2)–C(1)–N(1) 107.08(9).
amine-sulfonylimine complexes currently recorded in the
Cambridge Crystallographic Database, N-(((pentafluorophenyl)-
imino)sulfonyl)-quinuclidine (6)[15] and N-((cyanamido)-
sulfonyl)-1-methylpiperidine (7) (Chart 1).[16] The structures of
1, 2, and 3b are depicted in Figs 1, 2, and 3.
The geometry of the Burgess reagent is well modelled at the
G3MP2 level.[17] Selected bond distances from experiment and
theory are presented in Table 2. Heats of reaction in the gas phase
from the amine and sulfonylimine (the negative of the S–N bond
dissociation energy (BDE)) were calculated as DH(298 K) ¼
ꢀ33.5 kcal molꢀ1 for the NEt3 adduct and ꢀ34.2 kcal molꢀ1 when
triethylamine is replaced with NMe3. The corresponding gas
phase heats of formation are DHf(298 K) ¼ ꢀ161.8 kcal molꢀ1
for the Burgess reagent and ꢀ145.2 kcal molꢀ1 for the NMe3
derivative. Interestingly, the Burgess reagent (inner salt) com-
pounds 1 and 2, with their long, weak, dative amine-sulfonyli-
mine interaction, appear somewhat similar to dative amine-
borane interactions.[18,19] The corresponding G3MP2 B-N BDE at
298 K in H3BNMe3 is 38.0 kcal molꢀ1 which is in agreement
with experiment and the value of the B–N BDE for H3BNEt3
a long, weak-dative interaction may also be reflected in reactiv-
ity involving dissociation of the triethylamine moiety in the
Burgess reagent to reveal a sulfonylimine (O2S=NC(O)OR) that
quickly adds an alcohol to give the alkyl-N-carbomethoxysul-
famate. This latter alkyl-N-carbomethoxysulfamate subse-
quently undergoes an internal b-elimination to give an
olefin.[5] In addition, one notes that the degree of pyramidalisa-
tion of the sulfonylimine moiety is not particularly high when
compared with the chlorosulfonyl amide precursor 3b to the
Burgess reagent or its hydrosylates 4 and 5 (Table 1).
Overall, the structures of the Burgess reagents around
the sulfur centre resemble the only two other tertiary

Burgess Reagent Chemistry
869
is 35.9kcalmolꢀ1, both of which are similar to the S–N BDEs
given above.
hand, 1 and 2 are easily soluble in benzene, and 4 and 5 are not.
Gentle warming of 4 and 5 in vacuum did not transform them
back into 1 and 2 as reported by Atkins, and more aggressive
heating eventually led to extensive charring and decomposition
of the materials.
Burgess Reagent Reaction with Water
The ‘hydrate’ of the Burgess inner salt that was described in
Atkins’ Ph.D. thesis was reported to crystallise from moist
benzene.[11] Indeed, when water vapour is allowed to diffuse
into a dry benzene solution of 1 or 2, crystals form (respectfully
4 and 5). In the case of the water adduct 5, the melting point (89–
908C) and 1H NMR spectra agree well with the material reported
by Atkins. There is one notable difference in the proton NMR
spectra in that the broad 2-hydrogen resonance reported at d8.38
by Atkins appears as two resonances of equal intensity at d7.49
and 9.14 in the 600 MHz spectrum reported herein. These
resonances likely correspond to the two acidic (exchangeable)
NH protons in 5 that appear as an averaged resonance in the
60 MHz spectrum recorded by Atkins. The infrared spectra are
more difficult to compare because a limited selection of peaks
(without relative intensities) were reported by Atkins. None-
theless, there is agreement between some of the absorption
frequencies reported for the two samples. Based on the experi-
mental conditions and the physical and spectroscopic properties,
it appears likely that the material 5 reported herein and ‘hydrate’
reported by Atkins are one and the same. A very similar reaction
takes place with the methyl carbamate ester of the Burgess
reagent 1 and produces the adduct 4 that has very similar
spectroscopic properties to 5 and a slightly lower melting point.
Burgess’s inner salts 1 and 2 are only slowly soluble in water,
while compounds 4 and 5 dissolve quickly in water. On the other
X-Ray crystallographic structure analyses reveal the struc-
tures of 4 and 5 to be hydrolysates, not simple hydrates. Thus, the
overall reactions are irreversible hydrolyses (Scheme 2). Crys-
tals of hydrolysed ammonium methoxy- and ethoxycarbonyl-
sulfaminates may be obtained from benzene containing 1 %
water or by allowing water vapour to slowly diffuse into benzene
solutions of the Burgess reagents. The solid-state structures of
salts 4 and 5 consist of hydrogen-bonded triethylammonium
cations and alkoxycarbonylsulfaminate anion pairs. These
ammonium salt structures are depicted in Figs 4 and 5.
Although the spectroscopic characteristics described herein
for 4 and 5, and those reported by Atkins for the putative
‘hydrate’ appear consistent, there is one aspect of the report of
reversible formation of a hydrate by Atkins that remains
bothersome and that is the gentle dehydration of Atkins’
hydrate to reform the Burgess inner salt. Based on the X-ray
structures of 4 and 5 there is no doubt that these materials are
hydrosylates – not simple hydrates. As Atkins points out in his
Ph.D. thesis, his putative hydrate ‘dehydrated under conditions
milder than would be expected for the dehydration of’ the
ammonium salt 5. It remains possible that the structural and
spectroscopic characterisation of the isolated material are
different from the ‘hydrate’ as it is initially formed. Subsequent
dissolution in chloroform for characterisation and purification
might have led to the observed decomposition and the forma-
tion of the hydrosylate. Such a later-stage hydrolysis during
characterisation and purification could obscure the presence of
a very marginally stable hydrate. This could be the case if the
BDE of the S–N dative bound triethylamine is only slightly
higher than the BDE of the hydrogen bond(s) that bind the
water to the nucleophilic sites of the Burgess reagent in a
possible hydrate. This energetic ordering seems likely based on
the theoretical modelling studies described above. Work is
currently in progress to find even milder conditions to generate
a potential hydrate of the Burgess reagent that would require no
further manipulation to obtain samples suitable for spectro-
scopic and structural characterisation.
O3
O2
C1
S1
O4
N1
O1
Cl1
Fig. 3. Crystal structure of ethoxycarbonylsulfamyl chloride 3b (ORTEP
˚
drawings 50 % probability); selected bond lengths (A), S(1)–N(1)
1 % H2O
benzene, rt
O
O
O
O
O
O
1.6196(15), S(1)–O(3) 1.4133(13), S(1)–O(4) 1.4138(14), S(1)–Cl(1)
2.0161(7), N(1)–C(1) 1.388(2), C(1)–O(1) 1.213(2), C(1)–O(2); 1.319(2),
and angles (deg.), O(3)–S(1)–O(4) 121.62(9), O(3)–S(1)–N(1) 111.00(8),
O(3)–S(1)–Cl(1) 106.02(6), O(4)–S(1)–N(1) 105.96(8), O(4)–S(1)–Cl(1)
107.20(7), N(1)–S(1)–Cl(1) 103.60(6), C(1)–N(1)–S(1) 123.61(13),
O(1)–C(1)–O(2) 127.46(15), O(1)–C(1)–N(1) 123.41(16), O(2)–C(1)–
N(1) 109.13(14).
+
S
S
–
+
N
OR
Et3N
O
OR
N
–
Et3NH
H
1: R = CH3, 2: R = C2H5
4: R = CH3, 5: R = C2H5
Scheme 2. Hydrolysis of Burgess reagents.
Table 2. Geometries at G3MP2 (MP2(FULL)/6-31G(d)) level and experiment
˚
Distance [A]
Bond
1expt
1.901
1calc
2.060
1(Me3N)calc
N-carbomethoxy sulfonylimide
R3N-S
N=S
2.051
1.547
1.558
1.552
1.536
S=O
1.434/1.434
1.381
1.462/1.464
1.395
1.460/1.464
1.387
1.457/1.462
1.430
C–N
C=O
1.208
1.224
1.230
1.214

870
A. J. Arduengo III et al.
O3
C3
O2
O2
S1
N1
O5
C1
O1
C2
O3
C2
N1
C1
S1
O4
O5
O1
O4
1.89 Å
N2
C6
C8
C7
C5
C9
N2
C3
C7
C5
C6
C8
C4
C4
Fig. 5. Crystal structure of hydrolyzed ammonium ethoxycarbonylsulfa-
˚
minate 5 (ORTEP drawings 50 % probability); selected bond lengths (A),
Fig. 4. Crystal structure of hydrolysed ammonium methoxycarbonylsul-
˚
faminate 4 (ORTEP drawings 50 % probability); selected bond lengths (A),
S(1)–N(1) 1.6766(10), S(1)–O(3) 1.4510(8), S(1)–O(4) 1.4530(9), S(1)–
O(5) 1.4412(9), N(1)–C(1) 1.3680(15), C(1)–O(1) 1.2088(14), C(1)–O(2)
1.3513(14), and angles (deg.), O(3)–S(1)–O(4) 112.97(5), O(3)–S(1)–N(1)
101.47(5), O(3)–S(1)–O(5) 114.12(5), O(4)–S(1)–N(1) 106.12(5),
O(4)–S(1)–O(5) 114.09(5), N(1)–S(1)–O(5) 106.68(5), C(1)–N(1)–S(1)
123.71(8), O(1)–C(1)–O(2) 124.95(11), O(1)–C(1)–N(1) 126.09(11),
O(2)–C(1)–N(1) 108.97(9).
S(1)–N(1) 1.6821(9), S(1)–O(3) 1.4503(8), S(1)–O(4) 1.4522(8), S(1)–
O(5) 1.4375(9), N(1)–C(1) 1.3585(13), C(1)–O(1) 1.2138(13), C(1)–O(2)
1.3445(13), and angles (deg.), O(3)–S(1)–O(4) 113.06(5), O(3)–S(1)–N(1)
101.91(5), O(3)–S(1)–O(5) 114.82(5), O(4)–S(1)–N(1) 105.53(5),
O(4)–S(1)–O(5) 113.51(5), N(1)–S(1)–O(5) 106.62(5), C(1)–N(1)–S(1)
122.60(8), O(1)–C(1)–O(2) 124.53(10), O(1)–C(1)–N(1) 125.61(10),
O(2)–C(1)–N(1) 109.86(9).
DEPT135 and 2D NMR techniques (HSQC, HMBC, and
HHCOSY). Splitting types of protons are designated as s, d, t,
and q, for singlet, doublet, triplet, and quartet signals respec-
tively. Melting points were measured using a Yanaco Micro
Melting Point apparatus. IR Spectroscopy was conducted using
a FT/IR-4200 of JASCO equipped with MicromATRvision of
Czitek for measurement of the solid state and two NaCl plates
for measurement in CHCl3 solution. Relative intensities of IR
absorption were defined by w, m, s, and vs, to identify weak,
medium, strong, and very strong signals respectively. X-Ray
crystallographic analysis was performed by SMART APEX II of
Bruker AXS Co. Electrospray ionisation–mass spectrometry
(ESI-MS) was conducted on a Thermo Fisher Exactive Plus
Orbitrap Mass Spectrometer. Reagents and solvents for syn-
thesis were purchased from Tokyo Chemical Industry Co., LTD,
Kanto Chemical Co., INC., Wako Pure Chemical Industries,
Ltd, Sigma–Aldrich Co. LLC., Cambridge Isotope Laboratories.
Benzene, MeOH, EtOH, and triethylamine were used after
distillation over CaH2. Dried THF and Et2O were used from the
solvent cans of Kanto without any further purification.
Conclusion
The solid-state structures of methyl- and ethyl-carbamate esters
of the Burgess reagent exhibit weak dative bonding geometries
between the triethylamine and sulfonylimine units comprising
them. These geometric features include long N(triethylamine)–
S(sulfonyl) interactions and a sulfur coordination sphere that
is intermediate between tetrahedral and planar. These dative
N-S interactions are reproduced at the G3MP2 level of theory
and the calculated N-S bond dissociation energies are con-
sistent with the chemistry of the Burgess reagent towards
nucleophiles. Furthermore, the dative N-S interactions in the
Burgess reagent are reminiscent of dative N-B interactions in
amine boranes.
Ifa true‘hydrate’ ofthe Burgess reagent existsits stability isso
marginal that even simple sample manipulations at room temper-
ature lead to its transformation to hydrosylates. The spectroscopic
and physical data reported previously for this putative hydrate
actually correspond to
a hydrosylate (triethylammonium
N-(alkoxycarbonyl)sulfaminate). As expected, these triethylam-
monium N-(alkoxycarbonyl)sulfaminate do not easily revert to
the initial Burgess reagents.
Synthesis of Ethyl(chlorosulfonyl)carbamate 3b
Ethyl(chlorosulfonyl)carbamate 3b was prepared using a mod-
ification (substituting ethanol for methanol) of the Organic
Syntheses procedure published by Burgess et al.[2] Compound
3b was obtained as colourless crystals (mp 45.5–478C), yield
87 %. dH (600 MHz, CH3CN–acetone-d6) 1.13 (3H, t, JHH 7.2,
OCH2CH3), 4.13 (2H, q, JHH 7.2, OCH2CH3). dC (151 MHz,
CH3CN–acetone-d6) 14.84 (OCH2CH3), 65.70 (OCH2CH3),
150.7 (C=O).
Experimental
General
1H and 13C{1H} NMR spectra were recorded on a Bruker
Advance-II 600 (600 MHz for 1H and 151 MHz for 13C) spec-
trometer at room temperature with the inner standards of TMS
(dH 0.00), acetone-d6 (dH 2.06), CDCl3 (dC 77.0), and acetone-d6
(dC 30.6). Protons and carbons of products were assigned by

Burgess Reagent Chemistry
871
Synthesis of Methyl(carboxysulfamoyl)triethylammonium
Hydroxide 1
NCH2CH3, 3.68 (3H, s, CH3), 7.31 (1H, br s, SO2NHCO),
9.14 (1H, br s, NHCH2CH3), dC (151 MHz, CDCl3) 8.47
(NCH2CH3), 46.41 (NCH2CH3), 52.26 (OCH3), 153.7 (C=O).
nmax (CHCl3)/cmꢀ1 3422 (w), 3015 (m), 2954 (w), 1731 (m),
1457 (m), 1409 (m), 1336 (w), 1272 (m), 1216 (m), 1041 (m),
949 (w), 836 (w), 763 (vs), 756 (vs), 666 (m), 621 (m), 599 (w),
578 (w), 566 (w). nmax (solid)/cmꢀ1 3219 (w), 3051 (w), 3015
(w), 3000 (w), 2888 (w), 2760 (w), 1718 (m), 1467 (m), 1402
(m), 1360 (w), 1310 (w), 1266 (m), 1236 (m), 1203 (s), 1086
(m), 1065 (m), 1039 (s), 1013 (m), 898 (w), 831 (m), 782 (w),
730 (w), 701 (w), 685 (w), 675 (m), 662 (m), 624 (s), 586 (w),
569 (m), 555 (w). m/z (ESI, CH3CN, þve) 102.1281, calcd for
C6H16N: 102.1277. m/z (ESI, CH3CN, ꢀve) 153.9806, calcd for
C2H4NO5S: 153.9805.
Methyl(carboxysulfamoyl)triethylammonium hydroxide 1 was
prepared using the Organic Syntheses procedure published by
Burgess et al.[2] Compound 1 was obtained as colourless crystals
(mp 67.2–69.58C, lit[2] mp 71–728C), yield 63 %. dH (600 MHz,
CDCl3) 1.41 (9H, t, JHH 7.2, NCH2CH3), 3.47 (6H, q, JHH 7.2,
NCH2CH3, 3.70 (3H, s, CH3), dC (151 MHz, CDCl3) 9.38
(NCH2CH3), 50.43 (NCH2CH3), 53.26 (OCH3), 158.2 (C=O).
nmax (CHCl3)/cmꢀ1 3020 (w), 2951 (w), 1698 (m), 1460 (w),
1438 (w), 1342 (w), 1262 (s), 1222 (w), 1202 (w), 1187 (w),
1110 (w), 1039 (w), 965 (w), 866 (w), 734 (w), 714 (w), 668 (w),
623 (w), 590 (w), 577 (w), 563 (w). nmax (solid)/cmꢀ1 3046 (w),
2996 (w), 2979 (w), 2951 (w), 1719 (w), 1688 (m), 1455 (m),
1441 (m), 1402 (w), 1338 (w), 1326 (m), 1304 (w), 1241 (s),
1219 (m), 1186 (m), 1111 (m), 1092 (m), 1042 (m), 1023 (m),
960 (m), 893 (w), 856 (m), 835 (m), 787 (m), 717 (m), 695 (w),
679 (w), 668 (w), 651 (w), 641 (w), 627 (m), 600 (s), 577 (m).
Synthesis of Triethylammonium Ethylcarboxysulfaminate 5
Burgess reagent ethyl derivative 2 (203.2 mg, 0.805 mmol) in a
10 mL sample tube was dissolved in benzene (5 mL) with gentle
warming. The tube containing the solution of the Burgess
reagent was placed upright in a 100 mL round-bottom flask
equipped with a three-way stopcock. Water (50 mL, 2.8 mmol)
was added to the bottom of the flask (outside the tube containing
the Burgess reagent solution) via a 0.5 mL syringe. The round-
bottom flask was stoppered and stored at room temperature
under N2 for 21 h. The solid that crystallised from benzene in the
presence of water was collected by filtration. The residue in the
sample tube was rinsed with CHCl3 (10 mL ꢁ 2) to collect all
products. The solutions were transferred to another 100 mL
round-bottom flask by a Pasteur pipette and evaporated under
vacuum at 308C producing an oily residue that was stored at
room temperature under N2. After 1 day these oily residues
solidified. The combined solids were washed with hexane and
then dried under vacuum to provide the hydrolysed Burgess
reagent ethyl derivative 5 (107.5 mg, 0.398 mmol) in 49 % yield
as colourless crystals (mp 89–908C). dH (600 MHz, CDCl3) 1.24
(3H, t, JHH 7.2, OCH2CH3), 1.37 (9H, t, JHH 7.2, NHCH2CH3),
3.22 (6H, qd, JHH 7.2, 4.8, NHCH2CH3), 4.11 (2H, q, JHH 7.2,
OCH2CH3), 7.09 (1H, br s, SO2NHCO), 9.16 (1H, br s,
NHCH2CH3). dH (151 MHz, CDCl3) 8.48 (NHCH2CH3), 14.42
(OCH2CH3), 46.44 (NHCH2CH3), 61.21 (OCH2CH3), 153.3
(C=O). nmax (CHCl3)/cmꢀ1 3418 (w), 3223 (w), 3008 (m), 2805
(w), 2737 (w), 1726 (s), 1471 (m), 1443 (m), 1388 (m), 1356 (w),
1320 (w), 1269 (s), 1237 (s), 1199 (m), 1008 (m), 869 (m), 757
(w), 666 (m), 594 (m), 546 (s), 502 (m), 493 (m). nmax (solid)/
cmꢀ1 3250 (w), 3007 (w), 2789 (w), 2710 (w), 1721 (m), 1474
(m), 1442 (m), 1402 (m), 1384 (w), 1358 (w), 1261 (s), 1225 (s),
1200 (s), 1085 (w), 1039 (s), 1007 (m), 907 (w), 811 (m), 781
(m), 749 (m), 667 (m), 617 (s), 573 (m), 542 (m), 511 (w), 499
(w), 485 (m), 472 (w), 463 (w), 441 (m), 430 (w). m/z (ESI,
CH3CN, þve) 102.1281, calcd for C6H16N: 102.1277. m/z (ESI,
CH3CN, ꢀve) 167.9963, calcd for C2H6NO5S: 167.9961.
Synthesis of Ethyl(carboxysulfamoyl)triethylammonium
Hydroxide 2
Ethyl(carboxysulfamoyl)triethylammonium hydroxide 2 was
prepared using the Organic Syntheses procedure published by
Burgess et al.[2] Compound 2 was obtained as colourless crystals
(mp 81–828C, lit[1,11] mp 66–698C), yield 43 %. dH (600 MHz,
CDCl3) 1.285 (3H, t, JHH 7.2, OCH2CH3), 1.41 (9H, t, JHH 7.2,
NCH2CH3), 3.48 (6H, q, JHH 7.2, NCH2CH3), 4.13 (2H, q, JHH
7.2, OCH2CH3), dC (151 MHz, CDCl3) 9.34 (NCH2CH3), 14.29
(OCH2CH3), 50.34 (NCH2CH3), 62.06 (OCH2CH3), 157.6
(C ¼ O). nmax (CHCl3)/cmꢀ1 3023 (m), 2987 (m), 2948 (w),
2900 (w), 1687 (vs), 1461 (m), 1391 (m), 1367 (m), 1339 (vs),
1258 (vs), 1206 (s), 1170 (m), 1105 (vs), 1022 (m), 1041 (s),
1010 (w), 902 (w), 806 (w), 687 (w), 655 (w), 619 (m), 567 (w),
544 (w), 483 (m), 466 (m). nmax (solid)/cmꢀ1 2990 (w), 2945
(w), 2909 (w), 1718 (w), 1686 (s), 1470 (m), 1449 (m), 1398 (m),
1366 (m), 1325 (s), 1232 (vs), 1207 (s), 1181 (m), 1163 (m),
1095 (s), 1041 (m), 1019 (s), 899 (m), 866 (s), 812 (m), 792 (s),
739 (m), 718 (m), 599 (s), 576 (vs), 547 (s), 496 (m), 470 (w),
454 (w), 445 (w), 431 (m), 412 (w), 402 (s).
Synthesis of Triethylammonium
Methylcarboxysulfaminate 4
Burgess reagent methyl derivative 1 (199.9 mg, 0.839 mmol) in
a 10 mL sample tube was dissolved in benzene (5 mL) with
gentle warming. The tube containing the solution of the Burgess
reagent was placed upright in a 100 mL round-bottom flask
equipped with a three-way stopcock. Water (50 mL, 2.8 mmol)
was added to the bottom of the flask (outside the tube containing
the Burgess reagent solution) via a 0.5 mL syringe. The round-
bottom flask was stoppered and stored at room temperature
under N2 for 21 h. The solid that crystallised from benzene in the
presence of water was collected by filtration. The residue in the
sample tube was rinsed with CHCl3 (10 mL ꢁ 2) to collect all
products. The solutions were transferred to another 100 mL
round-bottom flask by a Pasteur pipette and evaporated under
vacuum at 308C producing an oily residue that was stored at
room temperature under N2. After 1 day these oily residues
solidified. The combined solids were washed with hexane and
then dried under vacuum to provide the hydrolysed Burgess
reagent methyl derivative 4 (183.6 mg, 0.719 mmol) as colour-
less crystals in 86 % yield, mp 87–898C. dH (600 MHz, CDCl3)
1.36 (9H, t, JHH 6.6, NCH2CH3), 3.22 (6H, q, JHH 6.6,
X-Ray Crystallographic Analyses
Crystal Data for Burgess Reagent 1
C8H18N2O4S (238.30 amu); data were collected on a colour-
less block obtained by slow evaporation of a THF solution
measuring 0.48 ꢁ 0.43 ꢁ 0.21 mm3. Data collection at ꢀ1538C
˚
with MoKa radiation (l 0.71073 A); monoclinic, P21/n, Z 4; a
˚
6.8066(5), b 12.8754(9), c 13.1397(9) A, b 93.8074(8)8; m(Mo)
0.280 mmꢀ1; with index ranges of ꢀ6 # h # 9, ꢀ17 # k # 13,
and ꢀ15 # l # 17; 6633 reflections were collected yielding
2741 independent reflections. The structure was solved by direct

872
A. J. Arduengo III et al.
methods and expanded using Fourier techniques (SHELX 2018).
All non-hydrogen atoms were refined anisotropically, while
hydrogen atoms were refined isotropically. Data to parameter
ratio 2741/140; R1 0.0274, wR2 0.0742 (I . 2s(I)); R1 0.0314,
wR2 0.0768 (all data); GOF 1.053. CCDC deposition number
1941098.
measuring 0.53 ꢁ 0.33 ꢁ 0.23 mm3. Data collection at ꢀ1538C
˚
with MoKa radiation (l 0.71073 A); triclinic, P-1, Z 4;
˚
a 8.4796(8), b 8.7778(8), c 10.2367(10) A, a 106.1971(12)8,
b 93.6684(12)8, g 108.6712(11)8; m(Mo) ¼ 0.245 mmꢀ1; with
index ranges of ꢀ11 # h # 9, ꢀ9 # k # 11, ꢀ11 # l # 13; 3993
reflections were collected yielding 3073 independent reflec-
tions. The structure was solved by direct methods and expanded
using Fourier techniques (SHELX 2018). All non-hydrogen
atoms were refined anisotropically, while hydrogen atoms were
refined isotropically. Data to parameter ratio 3073/166; R1
0.0269, wR2 0.0669 (I . 2s(I)); R1 0.0295, wR2 0.0686 (all
data); GOF 1.074. CCDC deposition number 1941102.
Crystal Data for Burgess Reagent (Ethylcarbamate Ester
Analogue) 2
C9H20N2O4S (252.33 amu); data were collected on a colour-
less block obtained by slow evaporation of a THF solution
measuring 0.51 ꢁ 0.50 ꢁ 0.33 mm3. Data collection at 238C
˚
with MoKa radiation (l 0.71073 A); monoclinic, P21, Z 2;
Crystallographic Data
˚
a 6.6023(9), b 12.8477(17), c 7.8470(10) A, b 106.2153(16)8;
m(Mo) 0.256 mmꢀ1; with index ranges of ꢀ8 # h # 5, ꢀ17 #
k # 6, ꢀ10 # l # 9; 3796 reflections were collected yielding
2838 independent reflections. The structure was solved by direct
methods and expanded using Fourier techniques (SHELX 2018).
All non-hydrogen atoms were refined anisotropically, while
hydrogen atoms were refined isotropically. Data to parameter
ratio 2838/149; R1 0.0295, wR2 0.0691 (I . 2s(I)); R1 0.0326,
wR2 0.0710 (all data); GOF 1.044. The Flack absolute structure
parameter was 0.05(3), indicating refinement of the correct
configuration for solid state 2. CCDC deposition number
1941099.
Crystallographic data has been deposited with the Cambridge
Crystallographic Data Center for 1, 2, 3b, 4, and 5 as: CCDC
1941098, 1941099, 1941100, 1941101, and 1941102 respec-
tively. These latter data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cam-
bridge Crystallographic Data Centre, 12, Union Road, Cam-
bridge, CB2 1EZ, UK; Fax: þ44 1223 336033; or deposit@ccdc.
cam.ac.uk).
Supplementary Material
Final energy-minimised geometries for the structures selected
for G2MP2 modelling, X-ray single crystal diffraction data for
1, 2, 3b, 4, and 5 in tabular form, and images of relevant text and
structures from George M. Atkins’ Ph.D. thesis are available on
the Journal’s website.
Crystal Data for Ethyl(chlorosulfonyl)carbamate 3b
C3H6NO4ClS (187.60 amu); data were collected on a colour-
less plate obtained by slow evaporation of a benzene/hexane
solution measuring 0.50 ꢁ 0.32 ꢁ 0.05 mm3. Data collection
˚
at ꢀ1538C with MoKa radiation (l 0.71073 A); monoclinic,
Conflicts of Interest
˚
P21/c, Z 2; a 8.6823(14), b 9.5159(16), c 9.3527(15) A, b
The authors declare no conflicts of interest.
99.645(2)8; m(Mo) 0.734 mmꢀ1; with index ranges of ꢀ11 #
h # 5, ꢀ12 # k # 12, ꢀ12 # l # 12; 4334 reflections were col-
lected yielding 1813 independent reflections. The structure was
solved by direct methods and expanded using Fourier techni-
ques (SHELX 2018). All non-hydrogen atoms were refined
anisotropically, while hydrogen atoms were refined isotropi-
cally. Data to parameter ratio 1813/96; R1 0.0305, wR2 0.0659
(I . 2s(I)); R1 0.0416, wR2 0.0707 (all data); GOF 1.043. CCDC
deposition number 1941100.
Acknowledgements
All authors thank The University of Alabama for support of the StanCE
project (Technology for a Sustainable Chemical Economy). YU thanks
Kitasato University for its support. DAD thanks the Robert Ramsay Chair
Fund of the University of Alabama for support. The computational work was
supported by the DOE BES Catalysis Program by a subcontract from Pacific
Northwest National Laboratory (KC0301050-47319). The authors are
especially grateful to George Atkins and Donald VanDerveer for helpful
discussions.
Crystal Data for Triethylammonium
Methylcarboxysulfaminate 4
References
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˚
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independent reflections. The structure was solved by direct
methods and expanded using Fourier techniques (SHELX 2018).
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Crystal Data for Triethylammonium
Ethylcarboxysulfaminate 5
C9H22N2O5S (256.32 amu); data were collected on a colour-
less block obtained by slow evaporation of a benzene solution

Burgess Reagent Chemistry
873
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Georgia Institute of Technology. From page 42: ‘The inner salt XXXI
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