Cala, Jean Kathleen B.
Vera Cruz, Aika Gail J.
*
*
*Solubility of organic compounds is a
property that provides information
regarding the identity and the
structure of the substance such as its
functional groups and what elements
it contains. Solubility depends on
various factors such as the nature of
the solute, temperature, and
pressure.
*In general, the tendency of a solute
to dissolve in a solvent basically
depends on the ability of the solute
to interact effectively enough with
the solvent molecules.
*The dissolving process involves
breaking of attractive forces among
solute and solvent particles, but the
breaking of the forces between the
solute particles and the solvent
particles is also observed.
*Polarity is one great factor for it
determines what reacts with what as
indicated in the “Like dissolves like”
principle.
*A polar solute dissolves in a polar solvent
because they interact with each other
through dipole-dipole.
*Nonpolar solutes and nonpolar solvents
interact with each other through London
dispersion forces (LDF). The presence of an
acidic CO2H or basic NH2 group in a water-
soluble compound can be detected by low
or high pH, respectively, of the solution.
*
*In the experiment, the solubilities
of 14 different organic compounds
were evaluated by testing it to
different solvent systems.
Different procedures were
conducted to solid and liquid
samples.
*
*About 30mg of each sample were obtained
in different test tubes. For every test
tube, 20 drops of the different solvent
systems were added. This was repeated
seven times for there are 7 solvent
systems to be tested. Each sample was
classified as completely soluble = +++,
partially soluble = ++, slightly soluble = +,
and insoluble = X, depending on its
reaction to the solvent.
*
Benzoic Acid
Sulfanilic Acid
Alanine
Phenol
OH
Salicylic Acid
*
*2 drops of each sample was obtained
in different test tubes. 20 drops of
the solvent was then added to the
test tube, as well. This was procedure
was repeated for each solvent. The
dissolution of the sample was
determined and classified as
completely miscible = +++, partially
miscible = ++, and immiscible = X.
*
Acetic Acid
Hexane
Benzamide
Aniline
Chlorobenzene
Ethylamine
Ethylacetate
Benzene
Cyclohexane
E-naphthol
*
Sample Water 5% NaOH 5% HCl 5%NaHCO3 Ether Conc.
H2SO4
85%
H2PO4
Alanine ++ +++ ++ ++ X X +
Aniline X X +++ X +++ +++ ++
Benzamide X X X + +++ ++ +
Benzene X ++ +++ +++ X X X
Benzoic Acid X +++ ++ +++ +++ + ++
Chlorobenze
ne
X +++ ++ +++ X + ++
Cyclohexane X X X X +++ X ++
Ethylamine +++ X +++ X +++ X X
Ethylacetate +++ +++ X ++ +++ X ++
Hexane X X ++ ++ +++ X X
E-naphtol X ++ +++ ++ +++ ++ +
Phenol ++ +++ +++ X +++ +++ X
Salicylic Acid X ++ +++ +++ +++ ++ +
Sulfanilic
Acid
+ +++ +++ +++ + ++ ++
*
Sample Water 5% NaOH 5% HCl 5%NaHCO3 Ether Conc.
H2SO4
85%
H2PO4
Alanine ++ +++ ++ ++ X X +
Aniline X X +++ X +++ +++ ++
Benzamide X X X + +++ ++ +
Benzene X ++ X +++ X X X
Benzoic Acid X +++ X +++ +++ + ++
Chlorobenze
ne
X +++ X +++ X + ++
Cyclohexane X X X X +++ X X
Ethylamine +++ X +++ X +++ X X
Ethylacetate +++ +++ X ++ +++ X ++
Hexane X X X X +++ X X
E-naphtol X ++ +++ ++ +++ ++ +
Phenol X +++ +++ X +++ +++ X
Salicylic Acid X ++ +++ +++ X ++ +
Sulfanilic
Acid
+ +++ +++ +++ X ++ ++
*
*
*In considering solubility in water a
substance is arbitrarily said to be
“soluble” if it dissolves to the extent
of 3g per 100mL of solvent.
*Water is a poor solvent for
hydrocarbons. The introduction of
halogen atoms does not alter the
polarity appreciably. Organic salts, on
the other hand, are water soluble.
*Acids and amines are generally more
soluble than neutral compounds.
*Branching of the alkyl chain of the
molecule lowers intermolecular forces
between its molecules, causing greater
solubility in water. This occurs simply
because the molecules of the branched
compound are more easily separated from
one another.
*Compounds with four or less carbons, and
which contain polar groups of oxygen,
nitrogen or sulfur, will often be soluble in
water. Compounds with five or six carbons
with those elements will often have
borderline solubility or be insoluble.
*
*Acids are soluble in 5% NaOH, a strong base, but
only strong acids are soluble in 5% NaHCO3, a
weak base.
*Strong acids: Carboxylic acids, sulfonic acids,
sulfinic acids, phenols with e-withdrawing
groups in the ortho- and/or para- positions
*Weak acids: phenols, some enols, imides,
primary and secondary nitro compounds,
arylsulfonyl derivatives of primary amines,
unsubstituted arylsulfonamides, oximes,
thiophenols
*Aldehydes and ketones are far too weakly acidic
to dissolve to any measurable extent in NaOH
solution.
*
*Aliphatic amines, primary, secondary, and
tertiary, form salts with hydrochloric acid.
Hence, they are soluble in dilute HCl.
*Aryl groups diminish the basicity of the
amine. Primary aromatic amines, although
more weakly basic than primary aliphatic
amines, are soluble in dilute HCl.
Diarylamines and triarylamines are not
soluble.
*Disubstituted amides (RCONR’2) which are of
sufficiently high molecular weight to be
water insoluble are soluble in dilute HCl.
*
*Ether is a slightly polar molecule.
*A compound that dissolves in both
water and ether means that it has both
a considerable nonpolar and polar
characteristics.
*Polyfunctional compounds and
derivatives as well as salts are too polar
to dissolve in ether while monofuctional
compounds are soluble in ether.
*
*Conc. H2SO4 is used with neutral, water-
insoluble compounds containing no elements
other than carbon, hydrogen, and oxygen.
*If the compound is unsaturated, is readily
sulfonated, or possesses a functional group
containing oxygen, it will dissolve in
concentrated H2SO4.
*Alkanes, cycloalkanes, and their halogen
derivatives are insoluble in concentrated
H2SO4.
*Simple aromatic hydrocarbons, and their
halogen derivatives do not undergo sulfonation
and are insoluble in concentrated H2SO4.
However, the presence of two or more alkyl
groups on the aromatic ring permits the
compound to be sulfonated.
*Phosphoric acid is not nearly as strongly acidic
as is sulfuric acid. It is capable of dissolving
most of the oxygen containing compounds such
as alcohols, aldehydes, and esters, but is not
able to dissolve unsaturated hydrocarbons such
as alkenes, alkynes or aromatics.
*
*The solubility or miscibility of a
solute to a solvent is generally
dependent on its nature. The
solubility classification of an
organic compound is based on its
composition, structure,
properties and presence of
functional groups.
*
*Construct a schematic diagram
for the determination of the
solubility characteristics of
organic compounds.
Wate
r
Soluble Ether
Insoluble Salts of organic acids, amine hydrochlorides, amino acids, polyfunctional compounds with hydrophilic functional groups: carbohydrates (sugars), polyhydroxy compounds,
polybasic acids, etc.
Soluble
Acidic – Monofunctional carboxylic acids with five carbons or fewer; arylsulfonic acids
Basic – Monofunctional amines with six carbons or fewer
Neutral – Monofunctional alcohols, aldehydes, ketones, esters, nitriles, and amides with five carbons or fewer
Insoluble 5% NaOH
Soluble 5%
NaHCO3
Soluble Strong organic acids: Carboxylic acids with more than six carbons; phenols with electron-widthrawing groups in the ortho and/or para
position(s); β – diketones (1,3 – diketones)
Insoluble Weak organic acids: phenols, enols, oximes, imides,
sulfonamides, thiophenols, all with more than five carbons; β – diketones; nitro compounds with α - hydrogens
Insoluble 5% HCl
Soluble Aliphatic amines with eight or more carbons; anilines (only one phenyl group attached to nitrogen); some
ethers
Borderline Miscellaneous neutral compounds containing nitrogen
or sulfur and having more than five carbon atoms
Insoluble Conc. H2SO4
Soluble 85% H3PO4
Soluble Alcohols, aldehydes, ketones, esters with one functional group and more than 5 but fewer than 9 carbons, ethers, epoxides
Insoluble Alkenes, alkynes, some aromatic
compounds
Insoluble Saturated hydrocarbons, haloalkenes, aryl
halides, other deactivated aromatic compounds, diaryl ethers
*
* Castro, A. (2009). Solubility of organic compounds. Unpublished manuscript,
Physical Sciences Department, De La Salle University - Dasmariñas,
Dasmariñas, Cavite.
* Classification of organic compounds by solubility. (2004, October 28).
Retrieved from
http://opencourseware.kfupm.edu.sa/colleges/cs/chem/chem303/files\3-
Lecture_Notes_CHEM-303_(Chapter_5).pdf
* Kelly, B. (1997, December 31). Organic qualitative analysis. Retrieved from
http://faculty.swosu.edu/william.kelly/pdf/qo3.pdf
* Shriner, R. L., Fuson, R. C., & Curtin, D. Y. (1965). The systematic
identification of organic compounds (5th ed.). New York: Wiley.
* Trainor, D., Huang, A., & Moyer, J. (2012). Procedure for determining
solubility of organic compounds. Retrieved
from http://www.wellesley.edu/Chemistry/chem211lab/Orgo_Lab_Manual/Ap
pendix/ClassificationTests/solubility.html