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CHAPTER - 3
INTRODUCTION
Cyclohexanone is a colorless, mobile liquid with an odor similar to that of
pepper mint and acetone. It was first prepared by the dry distillation of calclum
pimelate and later by Bouveault by the catalytic dehydrogenation of
cyclohexanol. It is used chiefly as a chemical intermediate and as a solvent for
resins, lacquers, dyes and insecticides.
The most important use of cyclohexanone is as a chemical ~ntermediate in
nylon manufacture : 97% of all cyclohexanone output is used either to make
caprolactam for nylon-6 or adipic acid for nylon-66. In the caprolactam process
cyclohexanone is converted to cyclohexanone oxime (mp, 89-90°C), which is
rearranged with sulfuric acid to E-caprolactam (mp, 69°C). The overall efficiency
is > 97%. In the production of adipic acid, cyclohexanone is oxidized w~th nitric
acid m the presence of catalysts. Cyclohexanone is also used as a solvent and
thinner for lacquers, especially those containing nitrocellulose or vinyl chloride
polymer and copolymers and as a general solvent for synthetic resins and
polymers. Cyclohexanone is an excellent solvent for insecticides and many other
similar materials. Cyclohexanone is used as a building block in the synthesis of
many organic compounds, such as pharmaceuticals, insecticides, and herbicides.
Cyclohexanone is used in the manufacture of magnetic and video tapes.
Cyclohcxmone oxime with molecular formula CJi,,NO the derivative of
cyclohexanone is a white crystalline solid that can be crystallized as prisms from
hydroarbom solvents. It has melting point 90.S°C and boiling point 204OC.
sublimes at room temperature. It is probably combustible. This chemical
compound is stable under normal laboratory conditions. This compound is the
most important commercial derivative of cyclohexanone.
It can be prepared by warming cyclohexanone with an aqueous mixture
of hydroxylamine hydrochloride and sodium bicarbonate. Large commercial
quantities of cyclohexanone oxime are used as the intermediate in the
preparation of caprolactam which is used to form nylon. This compound is used
as a drug (therapeutic agent). The oxime undergoes a Beckmann rearrangement
in the presence of sulfuric acid to give caprolactam. The cyclohexanone oxime
can also be reduced to a mixture of cyclohexylamine and dicyclohexylamine or
it can be hydrolyzed to cyclohexanone.
NMR spectra of some oximes were measured at natural isotopic
abundance in pyridine and acetonitrile solutions (I). The temperature
dependence of the FT-IR spectra of absorbed cyclohexanone oxime was studied
on pentasil zeolite (2). Thennodynamic properties like heat capacities of
crystalline and liquid cyclohexanone oxime were measured by vacuum adiabatic
calorimehy (6 - 300 K) and by the triple heat bridge method (300-450 K) (3). The
mrrangement of cyclohexanone oxime to e-caprolactam was investigated over
heterogeneous catalysts (4).
Jain and Sharma reported the mechanism of reaction of impurities such
as cyclohexanol, cyclohexanone, aniline and cyclohexanone oxime, during the
course of polymerisation of caprolactam. This ~ndicates that cyclohexanone
oxime's application in the manufacture of nylon (5). A simplified industrial
route for the synthesis of cyclohexanone oxime an intermediate in the
caprolactam process is described by Rofia (6). This chemical compound was
employed as an oxidant in redox polymerisation (7). Talukdar, Wong and Mathur
reported the use of solar energy for the photonltrosafion of cyclohexane for the
production of cyclohexanone oxlme hydrochloride, an intermediate for the
manufacture of caprolactam (8).
However, so far no work is reported on vibrat~onal spectra and analysis of
cyclohexanone oxime. The aim of the present work is to obtain all the vibrational
frequencies and to propose assignments for cyclohexanone oxime. Hence the
present investigation has been attempted for the first time to get more information
on the fundamental vibrations as well as to assign all of them using the normal
coordinate analysis through FT-Infrared and FT-Raman spectroscopy.
3.1 EXPERIMENTAL DETAILS
The FTIR spectrum of cyclohexanone oxime is recorded on Brucker
IFS 66V FTIR spectrometer in the region 4000-200 cm-I. The FT Raman
spectnun of the same compound is also recorded on the same instrument with
FRA 106 Raman mod& equipped with Nd : YAG laser source opelilting at
1.06 pn l i e with a scanning speed of 30 cm.' min-' of spectral width 20 cm-'.
The fiquencics for all sharp bands w a e accurate to f 1 cm.'. The structure of
the compound is shown in Fig.3.1. The recorded specbum of cyclohexanone
oxime is shown in Fig.3.2.
3.2 THEORETICAL CONSIDERATIONS
The molecular symmetry of the molecule helps to determine and classify
the actual number of fundamental vibrations of the system. The observed
spectrum is explained on the basis of C, point group symmetry. The 5 1 optically
active fundamental vibrations are distributed as T,,b = 35a' (in-plane) + 16a"
(out-of-plane).
All the modes are active in both Raman and Infrared. Assignments have
been made on the basis of relative intensities, magnitudes of the frequencies and
polarisation of the Raman limes. The vibrational assignments are discussed in
terms of the potential energy distribution which was obtained from the evaluated
constants.
3.3 NORMAL CO-ORDINATE ANALYSIS
The normal coordinate calculations have been performed to obtain
v~brational fiquencles and the potential energy distribution for the various
modes. In the normal coordinate analysis, the potential energy distribution plays
an important role for the characterisation of the relative contributions from each
internal coordinates to the total potential energy associated with particular normal
coordinate of the molkule.
The normal coordinate analysis is necessary for complete assignment of
the vibrational firquencies of larger polyatomic molecules and for a quantitative
description of the vibrations. The values of bond-length and bond-angles have
been taken h m allied molecules and Sutton table (9). Internal co-ordinates for
the out-of-plane torsional vibmtions are defined as mcoaunended by IUPAC. The
simple valence force field has been adopted for both in-plane and outsf-plane
vibmtions. The normal coordinate calculations have been performed using the
program of Fuhrer et aL, (10). The initial set of force constants have been taken
from the related molecules.
3.4 POTENTIAL ENERGY DISTRIBUTION
To check whether the chosen set of assignments contribute maximum to
the potential energy associated with normal coordinates of the molecules, the
potential energy distribution (PED) has been calculated using the relation
F,~L2,k
PED = - L
where F,, are the force constants defined by damped least square technique, L,,
the normalised amplitude of the associated element (i,k) and hi the eigen value
~mresponding to the vibrational frequency of the element k. The PED
Contribution comeqm~ding to each of the observed f-uencies over 10% are
alone listed in the present work.
3.5 RESULTS AND DISCUSSION
The observed frequencies along with their rtlative intensities of
cyclohexanone oxirne and probable assignments are presented in Table 3.1. The
assignment of fkequcncies is made as follows.
Stretching vibrations
C-H Stretching
In large numbered rings such as cyclohexane, the C-H stretching
absorptions are usually observed below 3000 cm". In the present case, the
absorption band observed at 2843,2889,2925 and 2977 cm" in the IR spectrum
and 2831, 2857, 2900, 2938, 2962, and 2988 cm-' in the Raman spectrum are
assigned to the C-H stretching present in the cyclohexane ring. The weak and
strong wave numbers correspond to symmetric and antisymmetric vibrations of
the C-H bond. The calculated wave numbers agree with the observed frequencies.
The present conclasion is in agreement with the literature values 111-141.
The PED calculation for C-H stretching indicates that all are pure modes
except at the calculated tkquency, at 2890 cm-I and 2849 cm" which are the
mixed modes with little contributions due to C-C stretching.
0-H stretching
In the the 0-H stretching band is of medium to strong intensity
although it may be broad. H o d e r , in in spectra, the band is
g 4 y weak The O-H &etching of the cyclohcxa~~ne oxime is assigned to
3 187cm-' which agrees with the calculated frequency at 3 18 1 cm-' [I 5-2 1 ]
C=N Stretching
For oximes, the C=N stretching band occurs in the region 1690-1 620 cm*' .
In the present case, it is assigned to strong infrared at 1669 cm" which agrees
with the calculated frequency at 1664 cm" and literature value [22].
C-C Stretching
The skeletal vibration of alkane are often weak in inkxed and usually of
weak to medium intensity in Raman spectra. The C-C stretclung absotptions
occur in the region 1260-700 cm-'. Thus bands observed at 1225, 1214, 1138,
11 10, 1095 and 1088 cm-' are assigned to six C-C stretching vibrations and they
are in agreement with the calculated fi-equencies.
In plane and out of plane bendings
C-H bending
The C-H in plane bending vibration in cyclohexane rings is usually
observed in the region between 1000 - 1400 cm-' which is normally weak while
the C-H out of plane vibrations occuning between 700 - 1000 cm-' is normally
Strong. With this observation, the bands at 1239, 1250, 1264, 13 19, 133 1, 1339,
1350, 1436, 1458 and M80 cm-' are assigned to C-H in plane bending while the
bands observed at 482,656,794,838,850,868,900,919,93 1, and 950 cm-' are
assigned to GH out of plane bending vibrations. These bending vibrations due to
the C-H bond well agree with the calculated fresuencies as shown in table 3.1
and with the literature values [23,24].
Ring breathing
The CCC trigonal bending and CCC ring breathing vibrations are assigned
to 1019 and 995 cm-' respectively which agree with calculated values at
101 1 cm'l and 992 cm-'. This conclusion is in good agreement with the literahue
values [25].
Conclusion
A complete vibrational spectra and analysis is reported in the prtsent work
for the fitst time for Cyclohexanone oxime. The close agreement between the
obsewed and calculated frequencies confirm the validity of the present
assignment.
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