Dr.Farshid Zand
Organic Chem 233 L
Department of chemistry
San Diego Mesa College
CLASSIFICATION TESTS
A. ACIDS
There are relatively few suitable tests for carboxylic acids. Classification is based
mostly upon solubility tests. If the compound is water soluble, test the aqueous solution
of your compound with pH paper (also check the pH of the original water). If the
compound is water-insoluble and it dissolves in 5% (1.5M) sodium hydroxide and 5%
NaHCO3 solutions as performed in your solubility tests, it can be classified as a
carboxylic acid. Establish an equivalence value for the unknown to estimate its molecular
weight.
The equivalent weight or neutralization equivalent for the carboxylic acid can be
obtained from the base. It is most important that you accurately weigh your sample of
acid and titrate to a phenolphthalein (colorless to pink color) end point using an
accurately known dilute solution of sodium hydroxide (0.1000 M). If your unknown is
soluble in a greater than 50% ethanol/water mixture, then use bromothymol blue as the
indicator to give a yellow to blue color change.
Using an analytical balance, accurately weigh out approximately 0.2 g of your
unknown acid (measured to 0.001g) and dissolve in 50 – 100mL of water. It may be
necessary to warm the solvent to affect complete dissolution. Add a drop or two of
phenolphthalein indicator and titrate to an end point with an accurately know
standardized solution of sodium hydroxide, usually 0.1000M. If your unknown is
insoluble in water, dissolve 95% ethanol or a water/ethanol mixture. If ethanol is the
major solvent, use bromothymol blue as the indicator, since it gives a sharper endpoint
than phenolphthalein. Te equivalent weight can be calculated from the following
equation:
B. ALCOHOLS
1. Ceric Nitrate – A qualitative test for alcohols and phenols.
a. For Water-Soluble Compounds
Add 0.5 mL of the ceric nitrate reagent to 2-3 mL of distilled water in
a test tube, and mix thoroughly. Add 1 to 2 drops of the compound to
be tested, shake, and note the color. If the compound is a solid, first
dissolve it in water then add 4 to 5 drops of the aqueous solution to the
reagent.
b. For Water-Insoluble Compounds
Add 0.5 mL of the ceric nitrate reagent in a test tube to 3 mL of dioxane.
Should the solution become colorless add more ceric nitrate reagent until
the color persists. If a precipitate forms, add water (3 to 4 drops), with
shaking, until the solution is clear. Add 1 to 2 drops of the compound to
bed tested, shake and note the color. If the compound is a solid, dissolve it
in dioxane and the and 4 to 5 drops of dioxane solution to this reagent
Classification Test 1
Dr.Farshid Zand
Organic Chem 233 L
Department of chemistry
San Diego Mesa College
A positive test for an alcohol is indicated by a change in the color
of the reagent from yellow to red. Phenols give a brown to green-brown
precipitate in aqueous solution; a very deep red to brown coloration is
formed in dioxane.
A positive test is obtained with alcohols and phenols containing no
more than ten carbons. With larger molecules too little color is given for
the test to be reliable.
2. Chromic Anhydride - A qualitative test for primary and secondary alcohols.
To 1 mL of acetone in a small test tube, add 1 drop of a liquid or about 40
mg of a solid compound. Then add 1 drop of the chromic acid – sulfuric acid
reagent and note the result within 2 seconds. Run a control test on the
acetone.
A positive test for primary or secondary alcohols consists in the
production of an opaque suspension with a green to blue color. This test can
be used to oxidize a secondary alcohol to a ketone which can then be
converted into the corresponding 2,4-DNP derivative for identification.
Tertiary alcohols give no visible reaction in 2 seconds; the solution remains
orange in color. Disregard any color changes after two seconds. This test may
also be used to distinguish between aldehydes and ketones.
3. Lucas Test - A qualitative test for distinguishing between primary, secondary,
and tertiary alcohols. This test is restricted to water soluble alcohols.
To 0.5 mL (or less) of the alcohol, quickly add 3 mL of the Lucas Reagent
(hydrochloric acid- zinc chloride) at 26 – 27 °C. Close the tube with a cork
and shake; then allow the mixture to stand. Observe carefully for the first five
minutes; land intermittently for up to one hour. Note the time required for
reaction to take place, as indicted by the cloudy appearance of the solution,
and whether or not two immiscible layers finally separate. If the result is
positive forming to immiscible layers, carry out a second test using
concentrated hydrochloric acid, instead of the Lucas Reagent.
The differentiation is based upon the rate of formation of alkyl chlorides
from the alcohols. Tertiary alcohols react very quickly to give the alkyl
chloride, as indicated by the development of a cloudy appearance; the chloride
is sparingly soluble in the reagent and soon forms a distinct layer. (Secondary
alcohols react within 5 – 10 minutest give a cloudy appearance, and a distinct
layer appears later. Saturated primary alcohols do not react at ordinary
temperatures, and the solution remains clear. With concentrated hydrochloric
acid alone, tertiary again react rapidly to form the chloride, while a secondary
( or primary) alcohol remains clear, since neither will form an alkyl chloride
under the condition of the test.
4. Iodoform Test- A qualitative test for methyl carbinols (alcohols) and methyl
ketones
See Ketones, #3
C. ALDEHYDES
1. 2,4-dinitrophenylhydrazones - A qualitative test for aldehydes and ketones.
Place 1 mL of the 0.283 M dinitrophenylhydrazine reagent in phosphoric acid and
15 mL of 2 M hydrochloric acid in a 50 mL Erlenmeyer flask. Dissolve 1 or 2 drops
Classification Test 2
Dr.Farshid Zand
Organic Chem 233 L
Department of chemistry
San Diego Mesa College
of the unknown being tested in 3 mL of non-denatured 95% ethanol. Add the
ethanolic solution of the 2,4-dinitrophenylhydrazine hydrochloric acid solution with
stirring. If no precipitate immediately form, heat the reaction mixture to 50 – 60 °C
for five minutes and allow to stand for 15 -30 minutes. Generally the 2,4-DNP will
precipitate immediately on addition or on cooling. Occasionally the red reagent, 2,4dinitropenylhydrazine will precipitate out upon standing. This is readily confirmed by
its melting point (mp ca. 198-200°C with decomposition).
Most aldehydes and ketones yield solid insoluble 2,4-DNP’s. A positive test for
and aldehydes or ketone is the formation of a yellow, orange or scarlet precipitate.
The color is indicative of the degree of substitution. The saturated aldehydes and
ketones are typically yellow, while those carbonyls with a double bond or arene ring
in conjugation with the carbonyl groups are orange-red in color. If this test gives a
solid, save the precipitate – it can be used as a derivative.
2. Tollen’s Test – A qualitative test for aldehydes (also certain phenols and certain
aromatic amines)
In a thoroughly clean test tube place 2 mL of a 0.1 F solution of silver nitrate, and
add a drop of 3 M sodium hydroxide solution (approximately 10%), add a 2% dilute
solution of ammonia drop by drop with constant shaking, until the precipitate of silver
oxide just dissolves. In order to obtain a sensitive reagent, it is necessary to avoid
adding any excess of ammonia.
This reagent should be prepared just before use and should not be stored, since
the solution decomposes on standing and deposits a highly explosive precipitate.
To the Tollen’s Reagent prepared above , add a few drops of the unknown and
warm the tube gently in a water bath (important, do not over heat otherwise a false
positive test may result). If the tube is clean a silver mirror will be formed with an
aldehyde; if not, there will be no change in the solution or possible a black precipitate
of finely divided silver may appear if overheated.
The silver mirror is a positive test for aldehydes (or the other compounds listed
above , which must e ruled out by other means). The test involves reduction of silver
oxide to metallic silver (mirror) and oxidation of the aldehydes to the carboxylic acid.
It may be useful for you to carry out this test with known aldehydes since this test
sometimes is difficult.
D. AMINES
1. Hinsberg Test - A qualitative test for the presence and differentiation of primary,
secondary and tertiary amines. Note, you are only given primary amines in this
course.
To 8 – 10 drops of the unknown in a large test tube, add 10 mL of 2 M aqueous
potassium hydroxide and 14- 15 drops of benzenesulfonyl chloride ( Caution:
benzenesulfonyl chloride is a lachrymator). Stopper and shake the tube thoroughly and
note any reaction. The slowest reaction should be completed within 10 to 15 minutes If
the reaction is slow, warm the mixture very gently with shaking (do not boil) until the
disagreeable odor of benzenesulfonyl chloride can no longer be detected. The reaction
mixture should be alkaline at this point; if not, make alkaline to pH ≥ 13 using 2 M
potassium hydroxide. If two layers form, separate these and determine the solubility of
the organic layer in 5% hydrochloric acid. A tertiary amine will be soluble. Secondary
amines are not soluble as the N,N-dialkylbenzenesulfonamide. Cyclic or large primary
Classification Test 3
Dr.Farshid Zand
Organic Chem 233 L
Department of chemistry
San Diego Mesa College
amines may form N-alkylbenzenesulfonamide anions that have low solubility. The
protonation with hydrochloric acid gives the expected insoluble
Nalkylbenzenesulfonamide. This for all practical experiences is the same observations that
one would expect for a secondary benzenesulfonamide. To differentiate between large or
cyclic primary amines and secondary amines, the aqueous phase is separated and
acidified to pH 4 using concentrated hydrochloric acid. The formation of a precipitate
from the aqueous solution is strongly suggestive of a primary benzenesulfonamide.
Secondary and tertiary amines will not form a precipitate from the aqueous layer on
addition of acid. If the initial reaction mixture yields a homogenous solution, then a
soluble primary benzenesulfonamide is present. This is confirmed by acidifying to pH 4
precipitating the sulfonamide. The test involves the formation of benzenesulfonamides
from the benzenesulfonyl chloride and the primary or secondary amine. The following
equations should provide the information necessary to differentiate primary, secondary,
and tertiary amines. Note , only given primary amines are given in this concourse. If the
reaction gives a precipitate, save the solid as a derivative for its melting point.
Insert reactions here
E. KETONES
1. 2,4-Dinitrophenylhydrazones – A qualitative test for aldehydes and ketones. See
Aldehydes, #1.
2. If a compound gives a positive test for a carbonyl group (2,4-DNP) and negative tests
for an aldehyde, it is probably a ketone.
3. Iodoform Test – A qualitative test for methyl carbinols (alcohols) and methyl
ketones.
In a large test tube dissolve 4-6 drops, 0.1-0.15 g if a solid, of the unknown in
2mL of water with 2 mL of 3M sodium hydroxide solution. If the unknown is insoluble,
add sufficient dioxane to give a homogenous solution. Add drop wise (with shaking) 3mL
of the Iodoform iodine test solution. With some compounds, a yellow precipitate of
Iodoform appears almost immediately even when cold. If Iodoform does not appear
within 5 minutes, warm the solution to 60 °C in a beaker of hot water. If the brown color
persist for 2 minutes. Add a few drops of sodium hydroxide solution to remove the excess
iodine, dilute the mixture with 5 – 10 mL of water and allow it to stand for 10 minutes.
If the unknown contains a methyl ketone or methyl carbinols group, it is oxidized
to give the corresponding carboxylic acid and iodoform. Iodoform crystallizes as lemonyellow colored hexagons having a very characteristic odor and melting point of 119°C.
F. PHENOLS
1. Ferric Chloride Test – A qualitative test for phenols and enols.
Prepare a dilute solution of your unknown (about 1 drop in 1 mL H2O or if your
unknown is water insoluble in ethanol) and add this to several drops of 5% (0.5 M) ferric
chloride solution. Compare the color produced with that of pure solvent and a drop of
ferric chloride. Occasionally the color produced is not permanent; hence, care should be
taken to watch the solution closely at the instant the drop of ferric chloride is added.
The formation of a color, usually purple but also re, blue, or green colors may be
seen is typical of most phenols and enols. However, many of phenols do not give any
Classification Test 4
Dr.Farshid Zand
Organic Chem 233 L
Department of chemistry
San Diego Mesa College
color so a negative test must not be taken as significant without additional supporting
data.
2. Bromine Water – A qualitative test for certain phenols and aromatic amines.
Make a 1% aqueous solution, 1 drop in 2 mL of water. If the unknown is
insoluble in water use a water/ethanol mixture. If necessary, deprotonate the phenol with
sodium hydroxide to dissolve. Add saturated bromine water drop by drop until the
bromine color persists.
Phenols or amines which are not highly substituted or deactivated brominate
readily in bromine water to produce solid brominated derivatives. It is possible to form
more than one bromophenol derivative. Again, not all phenols brominate readily or form
an insoluble product, so that a negative test by itself is not significant. If a precipitate is
formed and the appropriate melting point is found, it can be used as a derivative.
G. UNSATURATION – Do these tests if unsaturated (alkenes and alkynes) compounds
are found in your list of possible compound.
1. Bromine in Caron Tetrachloride – A qualitative test for alkenes and alkynes.
Dissolve 2 drops or 50 mg of the unknown in 2 mL of carbon tetrachloride. Add a
5% solution of bromine in carbon tetrachloride drop by drop (with shaking) until the
bromine color persists for at least a minute.
This test for double and triple bonds should be used in conjunction with the
Baeyer’s Test (see below). If HBr is liberated, this is evidence that the disappearance of
bromine is due to substitution rather than addition. HBr can be detected by blowing
across the top of the test tube, which forms a fog, as does concentrated HCl on opening
its bottle.
2. Baeyer’s Test – A qualitative test for olefins and acetylenes.
To 2 mL of water or ethanol, add 2 drops of the liquid or 50 mg of the solid
unknown. Then add a 0.1 M potassium permanganate solution drop by drop with shaking
until the purple color of the permanganate persists. For a blank determination count the
number of drops that may be added to 2 mL of 95% ethanol before the color persist. A
significant difference in the number of drops required in the two cases is a positive test
for unsaturation.
Classification Test 5
Dr.Farshid Zand
Organic Chem 233 L
Department of chemistry
San Diego Mesa College
PREPARATION OF DERIVATIVES
Suitable derivatives for the purpose of identification are stable solids which melt between
50 – 250 °C, and which are readily prepared in good yields from unknowns to be identified. For
the purpose of this course, the directions given here are taken form Shriner, Fuson and Curtin
and modified for use in this course should prove adequate. However, due to the nature of these
general procedures, they may not be the “best” procedure for all unknown in this course. If you
are having problems preparing of isolating your derivatives it may be well worth your effort to
examine the procedures used to prepare, isolate and recrystallize the derivatives for your possible
unknowns by conducting a library search. Begin by searching either Dictionary of Organic
Compounds or the Merck Index for the original literature on each of your possible compounds.
The procedures given in the older literature may give you improved isolation or recrystallization
procedures as compared to the general methods given below. You may need to consult with your
instructor for additional guidance before making changes to the procedures.
Be sure to choose a derivative that will prove the identity of your compound. In many
cases, the preparation of a given derivative will not readily distinguish between two or more
possibilities of compounds with similar physical properties. Plan ahead so that valuable
laboratory time will not be wasted making useless derivatives.
The quantities of reagents employed should be measured or weighed (at least
approximately). The amounts given in the procedures can be scaled up or down as required. The
measured of small amounts given in the procedures can be scaled up or down as required. The
measuring of small amounts of liquids is readily accomplished by means of a one milliliter
calibrated medicine dropper. If refluxing is required, a 6 x ¾” test tube or a small Erlenmeyer
flask may be attached to a reflux condenser. In purification of the derivatives by recrystallization,
when a solvent is not given, small tests should be made to determine a suitable one or consult
literature. The derivatives must be well dried before taking a melting point and, where possible,
the derivatives should be recrystallized until the melting remains constant and is sharp. A point
to remember is that the general procedures outline here will not be successful for all compound –
some modifications may be required.
The supposed derivative should not be taken for granted. If in doubt, it deserves to be
confirmed by some test. I it melts close to the starting material or derivatizing agents; it has to be
proven that it is in fact a derivative. A Mixed melting point can be used reliably for this purpose.
NOTE: Dispose of any leftover derivatives in the container labeled “TEST REAGENTS
& PRODUCTS, DERIVATIVES, ‘KNOWN’ AND ‘UNKNOWN’ COMPOUNDS”.
A. ACIDS
1. Anilides, p-Toluides, p-Bromoanilides
insert reaction here
One gram of the acid or its sodium salt is mixed with 2 mL of thionyl chloride (Caution
– corrosive and a lachrymator!) in a test tube, and the mixture is heated (in the hood) under
reflux for 30 minutes. The mixture is cooled, a solution of 1 of 2 g of the amine (aniline, ptoluidine, or p-bromoaniline) in 30 mL of cyclohexane is added and the mixtures warmed on the
steam bath for 2 minutes. During this time a large amount of insoluble amine hydrochloride
Classification Test 6
Dr.Farshid Zand
Organic Chem 233 L
Department of chemistry
San Diego Mesa College
forms. This solid is removed by vacuum filtration and saved for possible use later. The
cyclohexane filtrate is washed successively with 2 mL of water, 5 mL of 1.5 M hydrochloric
acid, 5 mL of 1.5 M sodium hydroxide solution, and 5 mL of water in a separatory funnel. If a
precipitate forms during these washing, gentle warm the solution to redissolve. The cyclohexane
can be evaporated and the amide is recrystallized from water or aqueous ethanol. If little solid is
obtained after evaporation of the cyclohexane, dissolve the vacuum filtered amine hydrochloride
in 10 mL of water. Isolate the undissolved solid by filtration and combine this material with the
residue obtain in the cyclohexane fraction. Recrystallize this material as above.
2. Amides – Do not use this derivative with water soluble carboxylic acids.
Insert eqn here
One fram of the acid is heated under reflux with 5 mL of thionyl chloride (Caution –
corrosive and a lachrymator!) for 15 to 30 minutes in the hood. This ice-cold mixture is
poured slowly and cautiously (in the hood) into 15 mL of ice-cold , concentrated
ammonia. This may be a very vigorous reaction, use care! The solid amide is
collected on a filter, and purified by recrystallization from water or dilute ethanol. Use
minimal amounts of ice-cold solvent to wash the amide, otherwise significant amounts of
derivative will be lost.
3. Equivalence Weigh Determination
Using an analytical balance, accurately weigh out approximately 0.2 g of your
unknown acid (measured to 0.001 g) and dissolve in 50 – 100 ml of water. It may be
necessary to warm the solvent to affect complete dissolution. Add a drop or two of
phenolphthalein indicator and titrate to an end point with an accurately known
standardized solution of sodium hydroxide usually 0.1000 M. If your unknown is
insoluble in water, dissolve in 95% ethanol or a water/ethanol mixture. If ethanol is used
in greater than 50% then use bromothymol blue as the indicator, since it gives a sharper
endpoint than phenolphthalein. The equivalent weight can be calculated from the
following equation:
B. ALCOHOLS
1. Phenyl – and α-Naphthylurethans
Insert eqn here
It is essential that your alcohol unknown be free of water for this reaction to be
successful. Place one gram of your anhydrous (distilled) alcohol or phenol unknown in a
small round-bottom flask, with 0.5 mL of phenyl or α-naphthyl isocyanate
(lachrymators!) is added (take a clean and dry stoppered test tube to the storeroom to
obtain either of these moisture sensitive reagents). If the reactant is a phenol, the reaction
should be catalyzed by the addition of 2-3 drops of anhydrous pyridine. If a spontaneous
Classification Test 7
Dr.Farshid Zand
Organic Chem 233 L
Department of chemistry
San Diego Mesa College
reaction does not take place, affix a calcium chloride drying tube to the flask and warm
on the steam bath for 5 minutes. Then cool in a beaker of ice and scratch the sides of the
tube with a glass rod to induce crystallization. The urethane is purified by dissolving it in
5 ml of petroleum ether, filtering the hot solution, and cooling the filtrate in an ice bath.
The crystals are collected on a filter and dried; the melting point is then determined.
Since the isocyanate reagents are quite sensitive to water special care should be
taken to use and anhydrous (distilled) alcohol or phenol. Otherwise quite a bit of byproduct which is insoluble in the petroleum ether will be produced if wet. The 1,3-di(αnaphthyl)urea has a melting point of 293°C and 1,3-diphenylurea (carbanilide)has a
melting point of 237°C; if your product shows one of these melting points, it is not of
value and must be rejected. Repeat the preparation, taking greater care to maintain
anhydrous conditions.
2. Benzoates and p-Nitrobenzoates
Insert eqn here
It is essential that your alcohol unknown be free of water for this reaction to be
successful. One milliliter of the dry alcohol is dissolved in 3 mL of anhydrous pyridine,
and add 0.5 g of benzoyl or p-nitrobenzoyl chloride (take a clean and dry stoppered test
tube to the storeroom to obtain either of these moisture sensitive reagents). After the
initial reaction has subsided, the mixture is warmed over a low flame (avoid overheating)
for a minute and poured, with vigorous stirring, into 10 mL of water. The precipitate is
allowed to settle and the supernatant liquid is decanted. The residue is stirred thoroughly
with 5 ml of 5% sodium carbonate, removed by filtration, and purified by
recrystallization from alcohol.
3. 3,5-Dinitrobenzoates
Insert eqn here
In order that this reaction to be successful your alcohol must be dry. Mix about
0.15 g o 3,5-dinitrobenzoyl chloride (obtained from the storeroom using a clear and dry
stoppered test tube with 0.5 mL of the alcohol and 0.15 mL pyridine in a small round
bottomed flask . Add a reflux condenser, and boil the mixture gently for 30 minutes using
a water bath. Cool the solution and add 5 mL of 0.6 M aqueous sodium bicarbonate to
remove any 3,5-dinitrobenzoic acid, then cool in an ice bath until the product solidifies.
Collect the crude crystalline product. Recrystallize the product from petroleum ether or
aqueous ethanol. Your alcohol must be dry; otherwise the acid chloride will be converted
to 3,5-dinitrobenzoic acid. The acid has a melting point of 205 – 207 °C.
Classification Test 8
Dr.Farshid Zand
Organic Chem 233 L
Department of chemistry
San Diego Mesa College
4. Acetates
Insert eqn here
One gram of mono- or polyhydroxy compound is added to 10 mL of anhydrous
pyridine. Four grams of acetic anhydride is added with mixing. After initial reaction has
subsided, if any, the solution is boiled for 3-5 minutes with a reflux condenser attached.
The mixture is cooled and poured into 50-75 mL of ice water. The acetyl derivative is
isolated by filtration, washed with cold 5% HCl, and then with ice cold water. The solid
is purified by recrystallization from alcohol.
5. Oxidation of Secondary Alcohol
Another alternative is to oxidize the secondary alcohol using chromic acid to the
ketone and isolate the corresponding 2,4-DNP derivative. Mix 10 drops (0.1 g) of the
unknown alcohol with 10 drops of the H2CrO4 reagent. Allow the mixture to react for
about a minute. The mixture will have a muddy greenish-brown color. Add drop wise
concentrated aqueous NaHSO3 until there is no more precipitate present, although the
solution is a very dark blue-green. Add 20 mL of the general 2,4-DNP reagent. Filter the
resulting crystals and recrystallize as you would for a normal 2,4-DNP derivative. To find
the “unknown” melting point in the literature, relate the structures of the alcohol to that of
the ketone.
C. ALDEHYDES
1. 2,4-Dinitrophenylhydrazones
Insert eqn here
Place 4 mL of the 0.283 M 2,4-dinitrophenylhydrazine solution in phorphoric acid
and 60 mL of 2M hydrochloric acid is placed in a 125 mL Erlenmeyer flask. Dissolve
0.2-0.5 g of the unknown in 10 mL of non-denatured 95% ethanol. Add this ethanol
solution of the carbonyl compound to the 2,4-DNPH solution drop wise with stirring.
About ten minutes after addition is complete, add an additional 25 mL of 2M
hydrochloric acid and stir for half an hour. If no precipitate forms immediately heat the
mixture 50 -60 °C for five minutes and allow to stand for 15 -30 minutes. Generally the
derivative will precipitate immediately on addition of the reagent or on cooling. For
complete precipitation it may be necessary to add water to the reaction mixture until
cloudiness forms. Occasionally the red reagent, 2,4-dinitrophenylhydrazine will
precipitate out upon standing. This is readily confirmed by its melting point (mp ca. 198200°C with decomposition). Vacuum filter to collect the phenylhydrazone derivative
washing with 2 x 10 mL 2 M hydrochloric acid, 2 x15 mL water and 15 mL cold 95%
ethanol.
Recrystallize this derivative by dissolving in 7-8 mL hot 95% ethanol. If the
derivative readily dissolves, add water until it become cloudy or until a maximum of 2
mL is added. If the derivative does not dissolve, slowly add ethyl acetate until a
homogenous solution is afforded. It may be necessary to remove the red unreacted 2,4dinitrophinylhydrazine reagent via hot fluent paper filtration. Slowly cool to room
temperature to form crystals. In some cases this may require approximately 12 hours.
Classification Test 9
Dr.Farshid Zand
Organic Chem 233 L
Department of chemistry
San Diego Mesa College
2. Semicarbazones
Insert reaction here
(a) For Water-Soluble Compounds
One-half milliliter of the aldehyde or ketone, 0.5 g of semicarbazide
hydrochloride, and 0.8 g of sodium acetate trihydrate are dissolved in 5 mL of
water in a test tube. *The mixture is shaken vigorously, and the test tube is
placed in a beaker of boiling water for 5 minutes and then allowed to cool to
slightly above room temperature. It is then placed in a beaker of ice, and the
sides of the tube are scratched with a glass rod to induce crystallization. The
crystals of the semicarbazone are removed by filtration and recrystallized
from water or aqueous ethanol, 25 – 50%.
(b) For Water-Insoluble Compounds
One –half milliliter (0.5g) of the aldehyde or ketone is dissolved in 5 mL of
ethanol. Water is added until the solution is faintly turbid (cloudy); the
turbidity is removed with a few drops of ethanol. The n0.5 g of semicarbazide
hydrochloride and 0.8 g of sodium acetate trihydrate are added, and from this
point Procedure (a) is followed stating at the “*”. If your compound does not
form a turbid solution on addition of water, use procedure (a) adding only
sufficient ethanol to dissolve your unknown in the solution of semicarbazide
hydrochloride and sodium acetate trihydrate.
3. Oximes
Insert equation here
Approximately 0.5 g of hydroxylamine hydrochloride is dissolved in 5 mL of
water followed by 3 mL of 3 M sodium hydroxide solution and 0.5 g (0.5 mL) of the
aldehyde or ketone unknown. If the carbonyl compound is water insoluble, just
enough ethanol is added to the above mixture to give a clear solution. This mixture is
warmed on the steam bath for 10 minutes and cooled in an ice3 bath. In order to
hasten crystallization, the sides of te flask are scratched with a glass rod. Occasionally
the addition of a few milliliters of distilled water will assist in causing the ocime to
precipitate. The product may be recrystallized from water or dilute ethanol.
Certain cyclic ketones, such as camphor, require an excess of alkali and a longer
time heating. If a ketone fails to yield an oxime by either of the above methods, 1 g of
it should be treated with 1 g of hydroxylamine hydrochloride, 4 g of potassium
hydroxide, and 20 mL of 95% ethanol. The mixture is allowed to stand to permit
unchanged ketone to separate. Te solution is filtered, acidified with hydrochloric acid,
and solution is allowed to stand permitting the oxime to crystallize. The product is
recrystallized from ethanol or aqueous ethanol mixtures.
Classification Test 10
Dr.Farshid Zand
Organic Chem 233 L
Department of chemistry
San Diego Mesa College
D. AMINES – PRIMARY
1. Benzamides and p-Nitrobenzamides
In a 50 mL round-bottom flask, dissolve 0.5 g (0.5 mL) of the unknown amine in 5 ml
of anhydrous pyridine. Slowly add 0.5 mL of benzoyl chloride (lachrymator!) to this
solution. An excess of the benzoyl chloride is the most frequent reason for the failure of
this usually reliable reaction. With a drying tube fitted to the flask, heat the reaction
mixture to 60- 70°C for 30 minutes using a water bath. Then pour the mixture into 50 mL
of water. If a solid precipitates at this time, collect it via filtration, and when nearly dry
from filtering, dissolve the solid in 20 mL ether. If no precipitate is formed, extract the
aqueous mixture twice with 15 mL portions of ether and combine the ether extracts. In
either case, wash the ether solution of the derivative with equal volumes of 1.5 M HCl
the n0.6 M sodium bicarbonate solution. Dry this ether extract with anhydrous
magnesium sulfate, filter, and remove the ether by evaporation in the hood. The obtained
solid residue, which should contain the derivative, may be recrystallized from one of the
following solvents: cyclohexane-ethyl acetate, 95% ethanol or aqueous ethanol. It is
suggested that you check the literature for the best solvent to recrystallize your derivative.
2. Benzene- and p-Toluenesulfonamides
The reaction given under the Hinsberg Test (see Classification Tests) should be run
on a double scale, with the final product recrystallized from 95% ethanol. (An ethanolwater mixture may be used also; too much water will result in the precipitation of an oil
or gum).
3. Acetamides
Solubilize the amine unknown by forming the ammonium chloride salt by reacting
about 0.5 g of the unknown amine with 25 mL of 5% hydrochloric acid. The add small
portions of a 5% sodium hydroxide solution are added until the mixture becomes cloudy;
the turbidity is then removed by adding 2 to 3 mL of 5% hydrochloric acid. A few chips
office are added to cool reaction mixture, followed by 5 mL of acetic anhydride. The
mixtures stirred or swirled vigorously, and a previously prepared solution of 5 g of
sodium acetate (trihydrate) in 5 mL of water is added in one portion. Generally there is a
fast precipitation of the derivative, sometimes it is necessary to chill the mixture
overnight to crystallize.
Recrystallize the crude derivative from cyclohexane or a mixture of cyclohexane
and toluene. Note, this acetamide must be thoroughly dry before attempting the
recrystallization from these solvents. An ethanol-water mixture may also be used for
recrystallization. Melting point data for these derivates are not located in the text book,
but can be found in cited references.
E. KETONES
1. 2,4-Dinitrophenylhydrazones
See Aldehydes, #1.
2. Semicarbazones
See Aldehydes, #2
Classification Test 11
Dr.Farshid Zand
Organic Chem 233 L
Department of chemistry
San Diego Mesa College
3. Oximes
See Alcohols, #1.
F. PHENOLS
1. Phenyl- and α-Naphthylurethans
See Alcohol, #1.
2. Bromo Derivatives
A solution of potassium bromide and bromine in water is added slowly (with
shaking), to a solution of 1 g of the phenol dissolved in water, ethanol, acetone, or
dioxane. Just enough of the brominating solution is added to impart a yellow color to the
mixture that persists after mixing. This will take far more bromine solution than you
think. If an oil forms this indicates that you must continue to add more of the bromine
solution. Eventually the oil should form a yellowish- whit solid. Transfer the reaction
mixture to 50 mL of water in an Erlenmeyer flask, shake or stir vigorously to break up
the lumps of the bromophenol derivative. Isolate the product by filtration and washed
with a dilute solution of sodium bisulfite to remove the last traces of the bromine reagent.
The solid is a recrystallized from ethanol, ethanol-water mixture or dissolved. Another
method uses hot methanol and water is added drop wise until a permanent cloudiness
results. Then allow the mixture to cool to crystallize.
3. Acetates
See Amines, #1.
4. Benzoates
See Amines, #2.
5. 3,5-Dinitrobenzoates
See Alcohols, #3
CHECK-OUT!!
On the final laboratory period you will check-out. All items in your locker must be both
clean and dry. You will be given a blank yellow locker card and your inventory sheet. Write only
on the blank yellow card your lock serial number (it’s on the back of the lock) and the
combination, DO NOT FILL OUT ANY OTHER INFORMATION ON THIS CARD. Attach
yellow card to you lock. Arrange the items in you locker from left to right according to the order
listed on the white inventory sheet. All items must be dry and clean. If you are missing item, go
to the storeroom and check-out those items. After you have checked all items, ask your
laboratory instructor to check you out. If any item is missing, you will go to the end of the
waiting list to be checked out. If all is accounted for, place all items back into the locker. Be sure
that you have also turned in all your products and reports before leaving.
Classification Test 12