CLASSIFICATION TESTS FOR CARBOXYLIC ACIDS AND THEIR DERIVATIVES Cabalo, A.*, Cachuela, B., Casapao, C., Daa, C., !e Bele", #. Depa$%&e"% o' (ha$&ac), Facul%) o' (ha$&ac) "+e$s+%) o' Sa"%o To&as
ABSTRACT Carboxylic acids and their derivatives are organic compounds that bears an acyl group that may be attached to an electronegative atom such as oxygen, nitrogen or sulfur, or a substituent substituent (-Y) that can act as the leaving group in nucleophilic acyl substituion (S N Acyl) !n S N Acyl, carboxylic acids and their acid derivatives derivatives "ould act as an electrophile electrophile and "ould be attac#ed attac#ed by a nucleop nucleophile hile All All carboxy carboxylic lic acid derivatives derivatives if sub$ecte sub$ected d to hydroly hydrolysis sis "ould "ould produce their corresponding parent carboxylic acid Among all the acid derivatives acyl halides are the most reactive and amides are the least %he ob$ective of this experiment is to distinguish the different different carboxylic carboxylic acids acids and their derivati derivatives ves and to classify classify them accordin according g to their their reactivities reactivities Classification tests such as hydrolysis, alcoholysis, aminolysis and hydroxamic acid test test "as "as perfo performe rmed d on acetyl acetyl chlor chlorid ide, e, acetic acetic anhy anhydri dride de,, ethyl ethyl aceta acetate, te, aceta acetamid mide e and and ben&amide %he results has sho"n that positive results such as the odor, precipitate formed and evolution of a gas in hydrolysis "ould determine the presence of their carboxylic acids %his is true for acetyl chloride, acetic anhydride, ethyl acetate and ben&amide 'hile the odor of the resulting mixture in alcoholysis proves the presence of the ester that "as formed upon addition of ethanol to acetic acid, acetyl chloride and acetic anhydride ormation of a "hite precipitate in aminolysis of acetyl chloride and acetic anhydride is a positive result of the presence of an anilide anilide "hich "hich is acetani acetanilide lide ydroxa ydroxamic mic Acid Acid %est is used used to identify identify the presenc presence e of the functional functional group of esters and amides A positive positive result of red-purple colored solution "as seen in ethyl acetate and acetamide *verall, determining the reactivities of carboxylic acids and their derivatives can be obtained by performing different classification tests %his is made possible due to the difference in their substituents and the reagents used +++++++++++++ ++++++++++++++++++++ +++++++++++++ +++++++++++++ +++++++++++++ ++++++++++++++ ++++++++++++++ +++++++++++++ +++++++++++++ +++++++++++++ ++++++++++ +++ in rancid odor of sour butter and hexanoic INTRODCTION
acid in aroma of goats
Carboxylic Acid is a class of organic comp compou ound nd that that bear bears s a carb carbox oxyl yl grou group p igure 1 Structure of a Carboxylic Acid
(C**) %he carboxyl group is named as such because of the presence of a carbonyl group (C*) and a hydroxyl group (-*) %he chief and most obvious characteristic of carboxylic acids is their acidity %hey react "ith "ith bases bases such such as sodium sodium hydro hydroxid xide e to produce metal carboxylate salts, C* .-/0 /any carboxylic acids are found in nature such as acetic acid in vinegar, butanoic acid
Carb Carbox oxyl ylic ic comp compou ound nds s
Acid cid
that that bear bears s
deri deriva vati tive ves s
are are
an acyl acyl grou group p
(C*) bonded to an electronegative atom (*, N or S) or substituent (-Y) "hich is the leavi eavin ng
grou roup
in
a
nucle cleophilic ilic
acyl cyl
substitution (S N Acyl) %here are many acid deriv derivati atives ves #no" #no"n n but but the most most commo common n
ones are the acid halides, acid anhydrides,
undergo basic hydrolysis but in esters it is
esters and amines
also #no"n as saponification
!n a nucleophilic nucleophilic acyl substitution, an addit addition ion of a nucle nucleop ophil hile e initia initially lly forms forms a tertahedral intermediate that eliminates one
igure 5 2eneral /echanism of Acid Acid alide ydrolysis
of the t"o substituents (the leaving group) originally bonded to the carbonyl carbon
igure 6 2eneral /echanism of 4ster ydrolysis igure . 2eneral /echanism of SN Acyl
All
acid
derivatives
can
be
Acid halides are the most reactive
hydroly&ed to yield a carboxylic acid but the
carbo carboxy xylic lic acid acid deriv derivati atives ves %hey %hey can can be
cond condit itio ions ns re7u re7uir ired ed rang range e from from mild mild to
converted
severe
into
many
other
#inds
of
compounds compounds by nucleophilic acyl substitution substitution Alcoholysis Alcoholysis reactions are usually
mechanism
carried out in the presence of pyridine or sodium hydroxide to react "ith the hydrogen chlo chlori ride de form formed ed Acid cid hali halide des s and and acid acid anhydrides react "ith an alcohol to yield an ester A primary alcohol "ould react faster to igure 3 !nterconversions of carboxylic acid derivatives
yd ydroly rolysi sis s is a typ typica ical S N Acyl
an acid acid hali halide de or acid acid anhy anhydr drid ide e than than a secondary or tertiary alcohol
proc proces ess s and and is inti intiat ated ed by the the atta attac# c# of "ater %he hydroxide ion "ould attac# the carbo rbonyl nyl
grou roup
to
give ive
a
tet tetrah rahedra edrall
igure 8 2eneral /echanism of Alcoholysis
inte interm rmed edia iate te and and the the expu expuls lsio ion n of the the subst substitu ituen entt "ould "ould follo" follo" to produ produce ce the
Aminolysis is a chemical reaction in
carboxylic acid and a by-product by-product ydrolysis
"hich a compound is reacted "ith ammonia
of acid acid halid halides es and and acid acid anhy anhydri drides des can can
or an amine %he reaction of acid halides
undergo under normal conditions since they
and and acid acid anhy anhydr drid ides es to an ammo ammoni nia a or
are both very reactive 4sters and amides
amine "ill yield an amide
colle collecte cted d %he %he sampl samples es used used are acetyl acetyl chloride chloride,, acetic acetic anhydri anhydride, de, ethyl ethyl acetate acetate,, acetamide and ben&amide igure 9 2eneral /echanism of Acid alide Aminolysis
yd ydrox roxamic mic Acid cid
is a
class lass of
I.
Hydrolysis of Acid Derivatives A. Acyl
organic organic compoun compound d bearing bearing the function functional al group group
ydr ydrox oxam amic ic
Acid cid
or
Acid
prepa prepared red from from ester esters, s, acid acid chlor chloride ides s or acid acids s
and
anhydrides
C(*)N(* C(*)N(*) )1 "hich hich is usua usuall lly y
carb carbox oxy ylic lic
halides
chlor chloride ide and and acetic acetic anhy anhydri dride, de, 1=
ydroxa ydroxamate mate %est %est is a chemical chemical test that that
drops "ere cautiously added to the
dete detect cts s the the pres presen ence ce of the the func functio tiona nall
test tube filled "ith 1 m> of "ater A
groups of an ester and an amide A positive
"armi arming ng effec ffectt
resul resultt of red-pu red-purpl rple e color color sho" sho"s s that that an
resultin resulting g mixture mixture "as then divided divided
ester or an amide has been converted into a
into t"o portions %o %o the first portion,
hydroxamic acid
1 m> m> of
"as "as
note noted d %he %he
.? AgN* gN* 3 "as added added
orm ormat atio ion n
of
a
prec precip ipit itat ate e
"as "as
observed %o the second portion, 1 m>
of
sat saturat rated
NaC* C* 3
"as
added added An evolu evolutio tion n of a gas gas "as "as igure : unctional 2roup of a ydroxamic Acid
observed B. Esters %he %he samp sample le used for for the the
igure ; Structure of a ydroxamic Acid
%he ob$ectives of this experiment is
hydrolysis of esters is ethyl acetate
the the
!n a test tube of 1 m> ethyl acetate,
carboxylic acids and their derivatives and to
. m> of .6? .6? Na* Na* solu soluti tion on "as "as
distinguish
added %he mouth of the test tube
to
diff differ eren enti tiat ate e
the the
them
reac reacti tivi viti ties es
using
of
different
"as covered "ith a marble %he test
classification tests
tube tube "as "as then then heat heated ed in a boili boiling ng -ETHODOLO#Y
"ate ater bath for for
6 minu inutes tes %he
%he materials and e7uipments "ere
resul resultin ting g mixtu mixture re "as "as neutr neutrali ali&e &ed d
prepared and cleaned prior to the start of
"ith "ith 1=? 1=? Cl solutio solution n and and "ith "ith a
the the
"afting motion, the odor "as noted
experime rimen nt
to
preve reven nt
possib sible
contamination contamination eagents and samples "ere
C. Amides
%he %he samp sample le used for for the the
added
to
each
test
tube
%he
hydrolysis of amides is ben&amide
mixtur mixtures es "ere "ere sha#en sha#en for for severa severall
!n a test tube, 1 m> of ben&amide
minu minute tes s %he %he odor odor and and laye layers rs of
"as treated "ith 6 m> of 1=? Na*
ester formed "as observed
solution %he resulting mixture "as heated until it boils A piece of red
III. III.
Amino inolysi lysis s : Anilid lide Forma rmatio tion Acyl halides and Acid
litm litmus us pape paperr "as plac placed ed on the the
Anhydrides Anhydrides
mouth of the test tube to test the reaction of gas evolved %he litmus paper@s r@s
change
of
color
"as
observed II.
rior to the test 6 m> of "ater "as placed into t"o different test tubes !n one test tube of "ater, a mixture of .3 drop drops s acet acetyl yl chlo chlori ride de and and =6 =6 m>
Alcoholysis : Schotten-Baumann
anilin aniline e "as "as adde added d and and to the the secon second d
Reaction
test tube of "ater, a mixture of .-3 drops
A. Acetic Acid Acid
acetic anhydride and =6 m> aniline "as adde added d %he %he prec precip ipit itat ate e form formed ed "as "as
!n a test tube, a mixture of 1=
observed
drops of acetic acid, 1 m> ethanol and 6 drops of concentrated .S*5 "as placed in a "ater bath for t"o
I.
Hydro!amic Acid "est %his test "as performed on ethyl
min minutes tes %he odor of the este ster
acetate and acetamide %he samples did
formed "as observed
not undergo a preliminary test before the
B. Acyl
halides
and
Acid
anhydrides
test "as conducted !n a mixture of . m>
.
of alcoholic N .* Cl and 1 m> of 1/
%"o mixtures "ere prepared
B*, B*, . drop drops s of ethy thyl acet acetat ate e "as "as
prio priorr to the the test test and and the the samp sample les s
added !n another mixture of . m> of
used "ere acetyl chloride and acetic anhydride %o the first test tube, =6 m> ethanol, 1 m> of "ater and =. ml of acetyl chloride "ere mixed %o the
second
test
tube,
=6
m>
ethanol, 1 m> of "ater and =. m> of acetic acetic anhydri anhydride de "ere mixed mixed %"o %"o milliliters of .=? Na* solution "as
.
alcoholic N.* Cl and 1 m> of 1/ B*, . drops of acetamide "as added %he t"o resulting mixtures "ere heated in a boiling "ater bath for t"o minutes After heating, the mixtures "ere cooled *ne milliliter of 6? eCl3 "as added to
each mixture %he color of the resulting
effe efferve rvesce scence nce or the evolu evolutio tion n of carbo carbon n
solution "as observed
dioxid dioxide e oth oth acety acetyll chlori chloride de and and aceti acetic c anhydrid ride
RESLTS AND DISCSSION
sho"ed o"ed
a
bubblin ling
effe ffect
therefore both samples yielded a carboxylic %able %able 1 ydrolysis of Acyl halides and Acid anhydrides
Sample
'arming effect
Acetyl Chloride
'arm (0)
'hite ppt (0)
ubbling effect (0)
Acetic Anhydrid e
oom %emp (-)
%urbid solution
ubbling effect (0)
acid upon hydrolysis
igure 1= ydrolysis of Acyl alide and Acid Anhydride %est esults %able %able . ydrolysis of 4sters
Sample
*bservations
4thyl Acetate
lastic balloon odor
According to %able %able 1, acetyl chloride had a "arming effect "hen added to "ater
4thyl acetate is the ester of acetic
"hile acetic anhydride sho"ed none
acid and ethanol !n the experiment, experiment, since a
addi additi tion on of .? AgN* gN* 3, acet acetyl yl chlo chlori ride de
base base (Na* (Na*)) "as "as used used to hydro hydroly& ly&e e the the
sho"ed a formation of a "hite precipitate
sample sample a carboxyl carboxylic ic acid salt "as formed
"hile a turbid solution in acetic anhydride
but but the the salt salt "as "as easi easily ly conv conver erte ted d into into a
%he turbid solution of acetic anhydride may
carboxylic acid "ith the addition of the Cl
be due to the fact that is reacts slo"er than
4thyl acetate@s original original fruity odor became a
acetyl chloride
plastic balloon-li#e odor due to the formation
%he "arming effect present "as due to the the
forma rmation ion
form forma ation ion
of
under"en r"entt
acetic tic an
acid id
of the acetic acid and ethanol
%his
exotherma rmal
reaction Acetic anhydride did not sho" a "arming effect that may be due to possible contami contaminatio nation n or undesire undesired d experime experimental ntal errors
igure 11 ydrolysis of 4sters %est %est esults
%he addition of NaC* 3 determines the presence of a carboxylic acid A positive result
"ould
sho"
the
formation
of
%able %able 3 ydrolysis of Amides
Sample
*bservations
en&amide
ed to blue litmus paper
After treating ben&amide ben&amide "ith Na* and upon heating, the ammonia gas is given off "hich can be proven by the change of color of the litmus paper from red to blue
igure 1. ydrolysis of Amides
igure 13 >itmus aper esults
*bservations
Acetic Acid
%able %able 6 Alcoholysis of Acyl halides and Acid anhydrides
Sample
*dor
ormation of layers
Acetyl Chloride
ruity
None
Acetic Anhydride Anhydride
ruity
None
Acetyl chloride and acetic anhydride reacts "ith ethanol to yield the ester, ethyl ethanoate %he difference bet"een the t"o
%able %able 5 Alcoholysis of Acetic Acid
Sample
igure 15 Alcoholysis of Acetic Acid %est esults
is that they produced different by-products
lastic balloon balloon odor odor
Acetyl chloride "ould give off the hydrogen chloride gas "hile acetic anhydride "ould
Alcoholysis Alcoholysis
or
esterification esterification
and
hydro hydrolys lysis is are revers reverse e reacti reaction ons s 'hen 'hen acet acetic ic acid acid is sub$ sub$ec ecte ted d to etha ethano noll and and
prod produc uce e etha ethano noic ic acid acid %he %he frui fruity ty odor odor produced produced "as due to the ester formed since esters generally has s"eet pleasant smells
concent concentrate rated d sulfuric sulfuric acid it produced produced the ester, ester, ethyl ethyl acetate acetate Concentr Concentrate ated d sulfuric sulfuric acid "as needed as an acid cid cata cataly lys st because the reaction is slo" and reversible Conc Concen entr trat ated ed sulf sulfur uric ic acid acid "as "as used used to reduce the chances of the reverse reaction happening %he plastic balloon odor of the resulting mixture "as due to the formation of ethyl ethyl acetat acetate e %he %he rever reverse se reacti reaction on is found on table .
igu igure re 16 16 Alcoh lcohol olys ysis is of Acyl cyl Anhydrides %est %est esults
ali alide des s
and and
Acid cid
%able %able 8 Aminolysis of Acyl halides and Acid anhydrides
Sample
Appearance of recipitate
Acetyl Chloride
'hite ppt
dissolved
Acetic Anhydride
No ppt
(-)
solution
of A positive result is exhibited by a red-purple color solution According to %able 9, both ethyl acetate and acetamide turned into a bro"n turbid solution upon addition of 6?
eCl eCl3
%he %he
solu soluttion ion
"as
actu ctually lly
burg burgun undy dy in colo colorr "hic "hich h is a shad shade e of Anilides are amides in "hich the
reddish bro"n ro"n turbid solution "as an
hydrogen of the amido group is replaced by
incor incorrec rectt descr descript iption ion of the the actua actuall resul result t
phen phenyl yl %he %he "hit "hite e prec precip ipit itat ate e in acet acetyl yl
%his "as due to insufficient #no"ledge of
chlor loride
of
descr describi ibing ng colors colors %here %herefor fore e both both ethy ethyll
acetani acetanilide lide Acetic Acetic anhydrid anhydride e should should have
acetate acetate and acetami acetamide de sho"ed sho"ed a positive positive
sho"n a "hite precipitate for the reason that
result
is
due
to
the
formation
it "ill also produce acetanilide "hen reacted to aniline aniline A possible possible contamin contaminatio ation n must have lead to the incorrect result Acetanilide has a "ater ter solubility of 8;3 x 1= 3 milligrams per liter at 99 o ahrenheit or .6 o Celsiu Celsius s Aceta Acetanil nilid ide e is sligh slightly tly solub soluble le in "ater at room temperature that is "hy upon addition of "ater the precipitate dissolved
igure 19 ydroxamic Acid %est esults
CONCLSION !t can can be conc conclu lude ded d that that seve severa rall classi classific ficati ation on tests tests can be cond conduct ucted ed to differentiate the reactions of carboxylic acids and and thei theirr deri deriva vati tive ves s Nucl Nucleo eoph phil ilic ic acyl acyl
igure 18 Aminolysis of Acyl alids and Acid Anhydrides %est esults %able 9 ydroxamic Acid %est
Sample 4thyl Acetate Acetamide
turbid
ro"n
turbid
substitution is the main mechanism of "hich hydr hydrol olys ysis is,,
alco alcoho holy lysi sis s
and and
amin aminol olys ysis is
undergoes ydrolysis of acetyl chloride, acetic anhy anhydri dride de,, ethyl ethyl aceta acetate te and and ben&a ben&amid mide e sho" sho"ed ed
posi positi tive ve
resu result lts s
to
prov prove e
the the
presence of their carboxylic acid and their
by-pr by-prod oduc uctDs tDs Alcoh Alcoholy olysis sis of acetic acetic acid, acid,
etrieve etrieved d from November November .8, .=18, from
acetyl chloride and acetic anhydride sho"ed
httpGDD"""vanderbilteduDAnSDChemistr yDi&&oDChem..=bDCh.=pdf
posit positive ive result results s to prove prove the presen presence ce of their their ester ester Aminoly minolysis sis of acety acetyll chlori chloride de sho" sho"ed ed a posi positi tive ve resu result lt to prov prove e the the presence of the formation of anilide ostive resul results ts in hydro hydroxam xamic ic acid acid test test on ethyl ethyl acetate and acetamide proves the presence of their functional group !naccurate results may
have
been
due
to
possible
contami contaminatio nation n and error error in performi performing ng the experiment *vera verall ll
the
experime rimen nt
"as
a
success in achieving its ob$ectives REFERENCES E1F Chemi Chemical cal %ests sts for for
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E.F E.F !den !denti tifi fica cati tion on of
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