The solid dihydrate of N,N-dimethyl-n-tetradecylamine oxide

Article abstract of DOI:10.1107/S0108270102022862

Crystalline N,N-dimethyl-n-tetradecylamine oxide has been prepared by reaction of liquid N,N-dimethyl-n-tetradecylamine with 70% H₂O₂ in the presence of CO₂ as catalyst. The resulting soft low-melting solid was crystallized as the dihydrate, viz. C₁₆H₃₅NO·2H₂O. The extended hydrocarbon chains pack in a parallel fashion, with the N-oxide ends of the molecules forming hydrogen bonds with the water molecules in hydrophilic layers. The N - O distance is 1.411 (3) A.

Full text of DOI:10.1107/S0108270102022862

organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
and heavy alkyl-chain systems, also demonstrated the possi-
bility for the production of essentially solvent-free solid non-
hygroscopic powdered forms of these amine oxide surfactants
(Smith et al., 1991). Based upon elemental analysis and
indirect spectral evidence, it was postulated by these workers
that the actual form of these `solid' materials approximated
that of an alkyldimethylamine oxide dihydrate. Extensive
characterization of these amorphous powders provided much
useful data for the formulator, such as melting point, critical
micelle concentration (CMC), hydrophile±lipophile balance
data (HLB), and solubility data. To date, however, no direct
evidence for the exact physical and chemical structures of
these solvent-free solid species has been available. We have
determined the structure of the title compound, N,N-di-
methyl-n-tetradecylamine oxide dihydrate, (II), to better
characterize this family of compounds, to provide a more exact
understanding of the nature of one of its members, and, at
least inferentially, to shed light on the probable structures of
other homologues in this family.
ISSN 0108-2701
The solid dihydrate of N,N-dimethyl-
n-tetradecylamine oxide
Joe D. Sauer,a Hassan Y. Elnagara and Frank R. Fronczekb*
aAlbemarle Technical Center, Albemarle Corporation, PO Box 14799, Baton Rouge,
LA 70898, USA, and bDepartment of Chemistry, Louisiana State University, Baton
Rouge, LA 70803-1804, USA
Correspondence e-mail: ffroncz@lsu.edu
Received 1 November 2002
Accepted 11 December 2002
Online 11 January 2003
Crystalline N,N-dimethyl-n-tetradecylamine oxide has been
prepared by reaction of liquid N,N-dimethyl-n-tetradecyl-
amine with 70% H2O2 in the presence of CO2 as catalyst. The
resulting soft low-melting solid was crystallized as the
dihydrate, viz. C16H35NOÁ2H2O. The extended hydrocarbon
chains pack in a parallel fashion, with the N-oxide ends of the
molecules forming hydrogen bonds with the water molecules
The title compound, (II), was prepared by reaction of the
starting liquid amine, (I), with 70% H2O2 in the presence of
CO2 as catalyst (see reaction Scheme below). By using 70%
H2O2, the 30% available water is apparently suf®cient for
formation of the solid dihydrate as thin fragile plates. It is
fortuitous that the dihydrate is crystalline, as N,N-dimethyl-
alkylamine oxides are notoriously dif®cult to crystallize. None
are present in the Cambridge Structural Database (CSD;
Allen, 2002), except for trimethylamine oxide (Caron et al.,
1964). The structure of N,N-dimethylethanolamine N-oxide
(Maia et al., 1984) has also been reported. Ammonium salts of
N,N-dimethylalkylamines are common in the CSD, with ten
entries present for alkyl = n-tetradecyl.
Ê
in hydrophilic layers. The NÐO distance is 1.411 (3) A.
Comment
There is a paucity of structural data in the literature on fatty
amine oxides. These compounds are commercially important
surfactants because of their extensive use in detergents
(Maisonneuve, 1991) and surfactant compositions. As a class,
they have been both known and commercially available since
the mid 1960s (Devinsky, 1986). End uses for these materials
generally vary with respect to the length of the included alkyl
chain, with `light' chains (C8 and C10) being especially effective
in hard surface degreasers and specialty cleaners (Miller et al.,
1995), `medium' chains (C12 and C14) ®nding broad usage in
light-duty detergents and dishwash formulations (Edward,
1963), and `heavy' chains (C16, C18 and higher) having useful
properties in ®ber treatments, such as fabric softeners, anti-
static treatments, and hair-conditioner products (Shapiro,
1970).
The asymmetric unit for (II) is shown in Fig. 1 and selected
geometrical data are given in Table 1. The alkyl group is
extended and slightly bowed, with atoms C2, C13 and C14
Ê
lying 0.084 (3), 0.071 (3) and 0.064 (3) A, respectively, on one
side of the best plane of atoms C2±C14, while atoms C7 and
Ê
C8 lie 0.046 (4) and 0.058 (4) A on the opposite side of this
plane. The CÐC distances in the hydrocarbon chain vary in
Ê
the range 1.512 (4)±1.526 (4) A, with a mean value of
Generally, these tertiary amine oxides are manufactured,
supplied, and formulated as aqueous solutions. A major
departure from this trend was developed by workers at Ethyl
Corporation when they were able to produce a family of stable
easy-to-handle liquid and solid compositions with a broad
spectrum of tertiary amine oxides dissolved in non-aqueous
`solvents' or co-surfactants (Sauer et al., 1991; Hughes et al.,
1992). Additional work, at least with several of the medium
Figure 1
A view of the title compound, with displacement ellipsoids at the 50%
probability level. H atoms are shown as spheres of arbitrary radii.
o62 # 2003 International Union of Crystallography
DOI: 10.1107/S0108270102022862
Acta Cryst. (2003). C59, o62±o64

organic compounds
of the peroxide to the liquid amine. The amine oxidation process is
strongly exothermic and the reaction temperature was regulated by
the rate of peroxide addition (Elnagar, 2000). The resulting soft solid
(m.p. 317 K) was crystallized from ethyl methyl ketone.
Crystal data
3
C16H35NOÁ2H2O
Dx = 1.056 Mg m
Mo Kꢁ radiation
Cell parameters from 3471
re¯ections
Mr = 293.48
Monoclinic, P21/c
Ê
a = 22.782 (8) A
b = 8.110 (5) A
ꢂ = 2.5±26.0ꢀ
ꢃ = 0.07 mm
T = 100 K
Ê
1
Ê
c = 9.995 (5) A
ꢀ = 91.19 (2)ꢀ
V = 1846.3 (16) A
Z = 4
3
Ê
Plate, colorless
0.48 Â 0.17 Â 0.03 mm
Figure 2
The unit cell in the title compound. Only water H atoms are shown.
Data collection
Nonius KappaCCD diffractometer
(with an Oxford Cryosystems
Cryostream cooler)
! scans with ꢄ offsets
15 919 measured re¯ections
3508 independent re¯ections
1746 re¯ections with I > 2ꢅ(I)
Rint = 0.076
Ê
1.5180 (11) A. Most intrachain bond angles of the hydro-
ꢂmax = 26.0ꢀ
carbon chain fall within the narrow range 113.7 (3)±114.8 (3)ꢀ,
with N1ÐC1ÐC3 slightly larger and C1ÐC2ÐC3 slightly
Ê
smaller. The NÐO distance compares with a value of 1.404 A
(corrected for libration) in trimethylamine oxide (Caron et al.,
h = 28 ! 28
k = 10 ! 10
l = 11 ! 11
Ê
1964) and a value of 1.399 A (mean of three) in N,N-di-
methylethanolamine N-oxide (Maia et al., 1984).
Re®nement
Re®nement on F2
R[F2 > 2ꢅ(F2)] = 0.086
wR(F2) = 0.195
S = 1.06
3508 re¯ections
w = 1/[ꢅ2(Fo2) + (0.0530P)2
+ 1.8197P]
The unit cell is shown in Fig. 2, which illustrates the
hydrogen-bonded regions near x = 0, where the water mol-
ecules associate with the head-to-head hydrophilic ends of the
fatty amine N-oxide molecules. In the interior of the cell, the
parallel hydrocarbon chains interdigitate along the [010]
direction. The hydrophilic region is shown in Fig. 3. Each
water molecule donates two hydrogen bonds and accepts one,
linking the N-oxide groups into six-oxygen centrosymmetric
rings. These rings are further linked by H2OÁ Á ÁH2O hydrogen
bonds to form two-dimensional arrays (see Table 2 for
hydrogen-bond details).
where P = (Fo2 + 2Fc2)/3
(Á/ꢅ)max = 0.004
3
Ê
Áꢆmax = 0.32 e A
3
Ê
0.20 e A
196 parameters
H-atom parameters constrained
Áꢆmin
=
Table 1
Selected geometric parameters (A, ).
ꢀ
Ê
O1ÐN1
N1ÐC16
1.411 (3)
1.477 (4)
N1ÐC15
N1ÐC1
1.489 (4)
1.494 (4)
O1ÐN1ÐC16
O1ÐN1ÐC15
C16ÐN1ÐC15
O1ÐN1ÐC1
108.0 (2)
109.7 (2)
109.4 (3)
106.3 (2)
C16ÐN1ÐC1
C15ÐN1ÐC1
N1ÐC1ÐC2
C3ÐC2ÐC1
111.8 (3)
111.6 (3)
117.0 (2)
109.5 (2)
O1ÐN1ÐC1ÐC2
173.4 (3)
N1ÐC1ÐC2ÐC3
172.1 (3)
Table 2
Hydrogen-bonding geometry (A, ).
ꢀ
Ê
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
O1WÐH1WÁ Á ÁO1
O1WÐH2WÁ Á ÁO2Wi
O2WÐH3WÁ Á ÁO1
O2WÐH4WÁ Á ÁO1Wii
0.88
0.87
0.88
0.88
1.85
1.97
1.87
2.07
2.727 (3)
2.832 (4)
2.741 (4)
2.829 (4)
174
170
177
144
Figure 3
The hydrogen bonding in the title compound. Only the ®rst two C atoms
of the C14 chain are illustrated.
1
2
1
2
Symmetry codes: (i) 2 x; 1 y; z; (ii) 2 x; y
;
z.
H atoms on C atoms were placed in calculated positions, with CÐ
Ê
H distances in the range 0.98±0.99 A, and thereafter treated as riding.
Experimental
A torsional parameter was re®ned for each methyl group. Water H
atoms were located in difference maps, and their OÐH distances
were restrained. For all H atoms, Uiso = 1.5Ueq of the attached atom
for methyl and water H atoms or 1.2Ueq for all other H atoms.
The title compound was prepared by reacting liquid N,N-dimethyl-n-
tetradecylamine with 70% hydrogen peroxide in the presence of CO2
as catalyst. A blanket of CO2 was maintained throughout the addition
ꢁ
Acta Cryst. (2003). C59, o62±o64
Joe D. Sauer et al. C16H35NOÁ2H2O o63

organic compounds
Caron, A., Palenik, G. J., Goldish, E. & Donahue, J. (1964). Acta Cryst. 17,
102±108.
Devinsky, F. (1986). Acta Fac. Pharm. 40, 63±70.
Edward, E. L. (1963). Br. Patent No. 942 870.
Elnagar, H. Y. (2000). US Patent No. 6 121 490.
Farrugia, L. J. (1997). J. Appl. Cryst. 30, 565.
Hughes, K. G., Smith, K. R., Borland, J. E., Crutcher, T. & Sauer, J. D. (1992).
Proceedings of the New Horizons '92: A CSMA/AOCS Detergent Industry
Conference, Bolton Landing, New York, USA.
Maia, E. R., Peguy, A. & Perez, S. (1984). Can. J. Chem. 62, 6±10.
Maisonneuve, B. (1991). Kirk±Othmer Encyclopedia of Chemical Technology,
Vol. 2, 4th ed., pp. 357±368. New York: Wiley.
Data collection: COLLECT (Nonius, 2000); cell re®nement: HKL
SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL
DENZO (Otwinowski
& Minor, 1997) and SCALEPACK;
program(s) used to solve structure: SIR97 (Altomare et al., 1999);
program(s) used to re®ne structure: SHELXL97 (Sheldrick, 1997);
molecular graphics: ORTEP-3 for Windows (Farrugia, 1997).
The purchase of the diffractometer was made possible by
grant No. LEQSF(1999-2000)-ESH-TR-13, administered by
the Louisiana Board of Regents.
Miller, J. H., Quebedeaux, D. A. & Sauer, J. D. (1995). J. Am. Oil Chem. Soc.
72, 857±859.
Nonius (2000). COLLECT. Nonius BV, Delft, The Netherlands.
Otwinowski, Z. & Minor, W. (1997). Methods in Enzymology, Vol. 276,
Macromolecular Crystallography, Part A, edited by C. W. Carter Jr & R. M.
Sweet, pp. 307±326. New York: Academic Press.
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: SQ1004). Services for accessing these data are
described at the back of the journal.
Sauer, J. D., Smith, K. R. & Borland, J. E. (1991). US Patent No. 5 055
232.
Shapiro, S. H. (1970). Amine Oxides, in Kirk±Othmer Encyclopedia of
Chemical Technology, 3rd ed., p. 259. New York: Wiley.
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È
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ꢁ
o64 Joe D. Sauer et al.
C16H35NOÁ2H2O
Acta Cryst. (2003). C59, o62±o64