Chemistry Project: Evaluating DCM Solvent, Spectra of Mulls, KBr Disc

This report delves into three key areas relevant to chemical analysis and spectroscopy. It begins with an examination of dichloromethane (DCM) as an organic solvent, discussing its properties, applications, advantages, and limitations, including its toxicity and alternative solvents like ethyl acetate. The report then explores the preparation and analysis of spectra of mulls, comparing the use of Nujol and Voltalef 3S as mulling agents, highlighting their chemical inertness and suitability for infrared spectroscopy. Finally, the report addresses the use of potassium bromide (KBr) discs in preparing samples for infrared spectroscopy, emphasizing the importance of particle size, dryness, and the avoidance of contaminants like water and carbon dioxide to ensure accurate spectral data. The report also includes references to relevant research papers and books.

PROJECT

TABLE OF CONTENT
QUESTIONS ..................................................................................................................................1
2. Dichloromethane (DCM) as a solvent ...................................................................................1
3. Spectra of mulls in Nujol and Voltalef 3S ............................................................................1
4. Use of potassium bromide (KBr) for preparing disc ..............................................................2
REFERNCES ..................................................................................................................................4

QUESTIONS
2. Dichloromethane (DCM) as a solvent
DCM is colourless, mild sweet and volatile liquid which is popularly used as organic
solvent. It is immiscible with water but can dissolve various organic compounds which make it
suitable for extraction and separation of organic products (Zhang and et.al., 2015). DCM has low
boiling point which permits the functionality in heat engine which can extract mechanical energy
from minor temperature differences. The immiscible nature of DCM with volatility makes it
effective solvent. The density of DCM is higher than water and thus when it is used as solvent
for extraction of organic compound then it easily forms two distinct layer for the easy separation
of the compounds (Wang and et.al., 2015). Contrary to chloromethane, dichloromethane is
unreactive or chemically inert which makes it a suitable solvent and allow substitution reactions
in it. Despite having immiscible nature it is cable to dissolve a huge range of organic substances
which make it suitable solvent for the organic compounds.
However its toxicity act as significant limitation or disadvantage for its solvent
properties. It has high volatility and as a result it quickly builds toxic vapours in small spaces
and thus can event lead to deaths. Apart form the health and environmental hazards DCM is also
associated with certain limitations when it is used as process solvent. DCM has higher disposal
cost and containment and also requires chemical stabilisers which may cause interference.
Fisher chemical Ethyl Acetate ethanol 3:1 solution can be preferred or used as an
alternative solution for DCM (El Assal and et.al., 2017). As compare to dichloromethane, ethyl
acetate has lower toxicity or environmental concerns. It also eliminate the chemical stabilisers
based interference caused in DCM solvents. Thus ethyl acetate can suitably used as alternative
choice for DCM without compromising the chromatographic separation of compounds.
3. Spectra of mulls in Nujol and Voltalef 3S
Nujol: Nujol is brand name of mineral oil. This heavy paraffin oil which makes it chemically
inert and result in uncomplicated IR spectrum. It medicinal properties and is also used to obtain
the infrared spectrum of solids. For obtaining IR spectrum Nujol and sample is combined in
pestle and mortar to make thick suspension called mull (Shepel and et.al., 2015.). It is
sandwitched between Kbr or NaCl plates. The nujol layer gives protective coating so that during
acquisition of IR spectrum sample does not decompose. During sample preparation sample must
also be kept saturated from Nujol as it has dominating peaks which can result in erroneous
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spectra (Negrea and et.al., 2015). Thus it is very important to record the spectra of nulls in Nujol
so that actual sample peaks can be obtained in spectrum.
Voltalet 3S: It is brand name of polymer chlorotrifluoroethylene (PCTFE) which has excellenge
resistance to x-ray radiations and ultraviolet rays. It is chemically inert and insensitive to
moisture and water. Its chemical stability and water repulsion property make it suitable for
variety of applications such as in LCD panels, cryogenic seals, water vapour or moisture barriers.
Its chemical stability makes it useful as protective barrier against chemicals and for prefabricated
liner and coating in chemical applications (Kogawa, de Mello and Salgado, 2016). It exhibits the
properties such as good chemical resistance, non wetting and zero moisture absorption. The
fluorine content makes voltlef as suitable mulling agent. After the substance is properly
grounded it is mixed with voltalef, Nujol oil so that particles can be suspended in the mulling
agent. It is important that spectrum of voltalef must also be recorded so that its spectrum of mulls
can be distniguished from that of the substance.
4. Use of potassium bromide (KBr) for preparing disc
Kbr is transparent in the wavelengths from ultraviolet to infrared wavelengths. In the
high transmission region the compound does not have significant optical absorption. Thus Kbr is
also used as infrared optical winnow and general spectroscopy elements due to its wider range of
spectrum. However the particle size and dryness of Kbr plays an important role in IR spectrum.
Kbr has high solubility and property to absorb or adsorb by attracting water molecules present in
surrounding environment (hygroscopic nature). Thus due to this reason potassium bromide is
kept dry and is stored or placed in dry environment. The dryness and size are important factors
which influences the spectrum quality as well as accuracy (Levanov and et.al., 2016). Quality
spectrum can be obtained only when sample is made up of dry solvent (solution IR) and dry
Kbr. The additional bands particularly of water and carbon dioxide must be avoided because they
can absorb infrared radiations.
Thus it is mandatory to minimise their presence and for this purpose dryness serves as an
essential aspect. Similarly sloping baseline indicates the scattering or diffraction of
electromagnetic radiation as it interact with sample. This occurs when particle or sample in Kbr
pallet has larger size or its surface is not homogenous (Shepel and et.al., 2015). Thus to avoid
sloping baseline and improving baseline quality samples are grounded or their size is kept
particularly smaller.
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The spectrum quality can be improved if homogenous mixtures are used. For this purpose
grinding is performed so that fine powder of Kbr can be used. The fine powder enhances the
absorption of humidity (due to hygroscopic nature of potassium bromide) from air and thus in
certain ranges background is increased (Ismi and et.al., 2015). However excessive grinding of
Kbr is also not necessary. Similarly for obtaining nujol mull solid sample is grind and mixed
with mineral oil so that suspension can be prepared. The suspension is then placed in between
Kbr. The grinding allow effective dispensation of compound between plate which improves the
spectrum quality.
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REFERNCES
Books and Journals
El Assal, Z. and et.al., 2017. Comparative study on the support properties in the total oxidation
of dichloromethane over Pt catalysts. Chemical Engineering Journal, 313, pp.1010-1022.
Ismi, I. and et.al., 2015. Spectral characterization of PA–Cu under two polymeric forms and their
complex PA–Cu. J. Mater. Environ. Sci. 6(2). pp.343-348.
Kogawa, A.C., de Mello, N. and Salgado, H.R.N., 2016. Quantification of doxycycline in raw
material by an eco-friendly method of infrared spectroscopy. Pharmaceutica Analytica
Acta. 7(2). pp.463-466.
Levanov, A.V. and et.al., 2016. Interaction between gaseous ozone and crystalline potassium
bromide. Russian Journal of Physical Chemistry A. 90(7). pp.1312-1318.
Negrea, P. and et.al., 2015. THE STUDY OF INFRARED SPECTRUM OF CHITIN AND
CHITOSAN EXTRACT AS POTENTIAL SOURCES OF BIOMASS. Digest Journal of
Nanomaterials & Biostructures (DJNB). 10(4).
Shepel, D. and et.al., 2015. Method of infrared spectra registration of activated carbons in
potassium bromide pellets. Chemistry Journal of Moldova. 10(1). pp.113-115.
Wang, Y. and et.al., 2015. Highly active spinel type CoCr2O4 catalysts for dichloromethane
oxidation. Applied Catalysis B: Environmental. 165. pp.477-486.
Zhang, X. and et.al., 2015. Catalytic low-temperature combustion of dichloromethane over V–
Ni/TiO 2 catalyst. RSC Advances. 5(96). pp.79192-79199.
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