M.PHARM I YEAR
DEPT OF PHARMACEUTICAL SCIENCES
TOPICS TO BE COVERED
• SOLVENT USAGE
• SOLVENTS EFFECTS & GREEN CHEMISTRY
• GREEN SOLVENTS & ITS DEFINITION
• ENVOIRMENTAL TOXOCOLOGY
• DETERMINATION OF TOXICITY
• SPECIFIC HEALTH & ENVOIRMENTAL REQUIREMENT
• GREEN SOLVENTS IN GREE CHEMISTRY
• PHYSICAL & CHEMICAL PROPERTIES OF SOLVENTS
• APPLICATION OF GREEN SOLVENTS
SOLVENT USAGE :-
• Solvents are substances that are liquid during
application and will dissolve other substances,
which can be recovered unchanged on removal
of the solvent.
• Research in green chemistry is making
dramatic achievements in the design of
chemicals, chemical syntheses, and chemical
processes that are environmentally benign and
• The goal of green chemistry is to reduce the
hazards associated with products and
• Widely used throughout the chemical industry
– Synthetic Chemistry
• Reaction medium on laboratory and industrial scale
• Extensively used in work-up and purification (usually
more than for reaction medium)
– Analytical Chemistry
• Sample extraction and preparation (Spectroscopy)
• Chromatography mobile phase (HPLC, TLC etc.)
• Recrystallisation to purify compounds and prepare
crystals suitable for analysis
• Used much more widely than just synthetic
– Paints, adhesives
• Solvent usually removed by evaporation after
application leaving coating behind
• Coating removal
– E.g. Dry cleaning – extensive use of perchloroethylene, a
known cancer suspect agent, which also contaminates
– E.g. Coffee decaffeination (benzene, CH2Cl2)
• Is the substance really needed?
• Could alternate, less toxic substitutes be used?
• What are the risks versus benefits for continued use
of the agent?
• What is the environmental impact of the substance?
• Does the procurement of the agent deplete an
• Does existing technology permit the “final” disposal
of the substance?
• If used, do we have the technology to ensure the
“safe” use of the substance?
• Solvents as a Green Chemistry Tool :-
Through a combination of knowledge of the
nature of a chemical’s hazardous properties
with the ability to manipulate the chemical’s
structure, chemists possess the ability and
skill to mitigate the hazard.
• Selection of Solvents and Reaction
Selection of a solvent should be based not
only on any hazards that the chemical may
possess, but also on existing environmental
problems that its use may exacerbate.
SOLVENT EFFECTS & GREEN
In order to study the solvent effect we need an help of conceptual
basis such as:-
• Theories of molecular structures.
• Concept of polarity.
• Bulk properties
a) Dielectric constant
Green solvents & its definition
• GOALS OF GREEN CHEMISTRY:-
i. To reduce hazards associated with product & process, this is to
maintain not only quality of life but also technical achievements.
ii. Reduction of risk:
RISK= HAZARD × EXPOSURE.
Solvents define a major part of the environmental
performance of processes in chemical industry and
also impact on cost, safety and health issues.
The idea of “green” solvents expresses the goal to
minimize the environmental impact resulting from
the use of solvents in chemical production.
• An ideal green solvent must possess following criteria:
i. Must have human safety.
ii. Reduced hazard.
iii. Easily degradable.
iv. Provide high product yield.
• Criteria for solvent selection:
i. Must have less human & environmental absorption.
ii. Its environmental toxicity should be understood.
iii. Environmental fate should be understood.
Green Solvents in Green Chemistry:-
Water as a reaction medium
• One of the most obvious alternatives to VOCs.
• Cheap, readily available, and plentiful (in the
• Useful for certain types of reaction but limited
– Low solubility of organic substrates
– Compatibility with reagents
• Clean up of aqueous waste difficult
• Useful in biphasic processes in conjunction with
• Similar advantages to water
– Natural, cheap, plentiful (too much of it!)
– Available in >99.9% pure form, £70/$110 per 25kg.
– By-product of brewing, ammonia synthesis, combustion
• Already being adopted in a variety of commercial processes (see later)
• Non-toxic and properties well understood
– asphyxiant at high concentrations
• Easily removed and recycled, and can be disposed of with no net
increase in global CO2
– Simple product isolation by evaporation, to 100% dryness.
• No solvent effluent
• Potential for product processing (extraction, particle formation,
Ionic liquids (IL’s)
• Typically consist of organic cation (often ammonium or
phosphonium salt) and inorganic anion
• Usually only consider IL’s which are liquid at room
• Great variety of structures possible
• Very low vapour pressure – attractive alternative to
2.Choline chloride/Zinc chloride
Ionic Liquids as Reaction Media
• Diels-Alder reactions
• Alkylation reactions
• Hydroformylation reactions
• Friedel Crafts reactions
• Pd-mediated C-C bond formation
• Alkene polymerisation
T. Welton, Chem. Rev., 1999, 99, 2071.
Ethyl lactate – a renewable solvent
• Derived from processing corn
• Variety of lactate esters possible
• Renewable source (non-petrochemical)
• Attractive solvent properties
– Easy to recycle,
– Non-ozone depleting
– Good solvent for variety of processes
• Commonly used in the paint and coatings industry
– Potentially has many other applications.
• TOXICOLOGY: Its an study of harmful effects of drugs, chemicals
& chemical mixture on the living organism.
It includes various branches such as:-
a. Clinical toxicology.
b. Forensic toxicology
c. Environmental toxicology.
• ENVIRONMENTAL TOXICOLOGY is multidisciplinary science
involving many diverse areas:-
a. CHEMISTRY:- deals with characterisation of toxins.
b. PHARMACOLOGY:- deals with study of entry & distribution of
toxins in the body.
c. BIOCHEMISTRY:- deals with interaction & metabolism of toxins.
d. BIOLOGY:- deals with effect of toxins on environment.
DETERMINATION OF TOXICITY
• CAN BE DONE THROUGH FOLLOWING BRANCHES:-
i. Descriptive toxicology.
ii. Mechanistic toxicology.
iii. Regulatory toxicology.
iv. Determination through:-
• In- vivo testing
• In-vitro testing
SPECIFIC HEALTH &
• THIS INCLUDES:-
a. Toxic chemicals.
b. Carcinogens & reproductive toxins.
d. Ozone depletion.
e. Toxicity to aquatic life.
• TOXIC CHEMICALS:-
A solvent is considered to be toxic if-
oral LD50 < 50mg/kg.
Dermal LD50< 200mg/kg.
• CARCINOGENS & REPRODUCTIVE TOXINS:-
Carcinogens are defined as those chemicals listed in current edition of
“annual report on carcinogens”.
Reproductive are defined as those chemicals listed under ‘safe
drinking water & toxic enforcement act’ of 1986.
The solvent in should not be flammable.
The flash point of chemical should be above 100ºF.
• OZONE DEPLETION:
The solvent in use should not contain any-
CLASS-II ozone depleting substances listed in title VI of clean air
• TOXICITY TO AQUATIC LIFE: chemicals in use should not have
any effect on aquatic animals.
GREEN SOLVENTS FOR ACADEMIC
• Teaching both environmental issue and basic chemistry to non-science
Mainly environmental topics with chemical facts &
Basic chemistry with environmental points.
• Education for green chemistry must show chemical processes that
carry environmental negatives can be replace with less polluting
• Academics must provides goals for green research.
• Must provides green technologies that can replace target technology
• School & colleges must creates awareness about various hazardous
• Academics also must provides information to their employees through
‘material safety data sheet’(MSDS).
PHYSICAL PROPERTIES OF SOLVENT’S:-
• The physical properties of solvents greatly
influence the choice of solvent for a particular
• The solvent should be liquid under the
temperature and pressure conditions at which
it is employed.
• thermodynamic properties:- density & vapor
pressure, temperature & pressure coefficients,
as well as the heat capacity surface tension.
• transport properties:- such as viscosity,
diffusion coefficient, & thermal conductivity,
also need to be considered
• Electrical, optical, and magnetic
properties, such as the dipole moment,
dielectric constant, refractive index,
magnetic susceptibility, and electrical
conductance are relevant, too.
• Molecular characteristics, such as the
size, surface area, and volume, as well as
orientational relaxational times, have
appreciable bearing on the applicability of
a solvent or on the interpretation of
CHEMICAL PROPERTIES OF
• The chemical properties of solvents have obviously a
strong bearing on their applicability for various
• Structuredness of Solvents:-The volatility, viscosity,
diffusion coefficient and relaxation rates of solvents are
described quantitatively by their structuredness.
• Stiffness:-expressed by the cohesive energy density
• Openness:-the difference between its molar and
• Ordering:- This is the deficit of entropy of the liquid
solvent relative to the solvent vapor or the dipole
• Polarity in Molecules:-Dispersion Forces-
Molecules that have no permanent dipole
still have their electrons in movement.
• Polarization and Polarizability:-If the
molecules have a dipole but there is no
applied electric field, the dipoles are
• Dipole–dipole interactions between rotating
dipolar molecules are small.
Only for molecules with large dipoles, and
where hydrogen bonding is absent, such as
DMSO (dimethyl sulfoxide) and acetonitrile,
do dipole–dipole attractions contribute
significantly to molecular association.
• Dipole moments of some solvents:-
• Benzene 0
• DMSO 3.9
• Acetone 2.69
• Hydrogen fluoride 1.83
• Water 1.83
• THF 1.75
APPLICATION OF GREEN SOLVENTS:-
• New syntheses of Ibuprofen and Zoloft.
• Integrated circuit production.
• Removing Arsenic and Chromate from pressure
• Many new pesticides.
• New oxidants for bleaching paper and disinfecting
• Getting the lead out of automobile paints.
• Recyclable carpeting.
• Replacing VOCs and chlorinated solvents.
• Biodegradable polymers from renewable resources