Unknown Expt Functional Group Tests

Bromine/CCl4 test for ____________

alkenes

Flame test for _______ ____________

aromatic compounds

Beilstein test for ______ or ________ __________

Alkyl or aryl halides

Silver Nitrate test for ________ or _______ _________-

Alkyl or aryl halides

Chromic acid test for _______

alcohols

Lucas Test for _________

alcohols

Ferric Chloride test for ______

phenols

Bromine-water test for _______

phenols

2,4-Dinitrophenylhydrazine (DNP) test for ______ and _________

aldehydes and ketones

Chromic acid test for _______ and _________

aldehydes and ketones

tollens test for _________ and __________

aldehydes and ketones

Iodoform test for _______ and ________

aldehydes and ketones

Sodium bicarbonate (BaHCO3) test for __________ __________

carboxylic acid

Hinsberg Test for ________

amines

hydroxyl amine/ferric chloride test for ______

esters

Iron (II) hydroxide test for ________ ___________

nitro compounds

procedure for Bromine CCl4 test for _________

unknown + THF or CH2Cl + 5% bromine in CCl4 → shake and observe results

Bromine/CCl4 positive test for unsaturation results in

discharge of the bromine color (decoloration of the solution)

Bromine/CCl4 negative test for _______ results in

failure of the color of bromine to discharge in the solution

procedure for flame test for ______ __________

place unknown on a spatula and place it in a flame → observe nature of combustion, color of flame, and the presence or the absence of smoke

black sooty smoke in a flame test is

indicative of an aromatic species (some unsaturated molecules and very long chain alkanes may also give positive results)

absence of black sooty smoke in a flame test is

indicative of the presence of an aliphatic compound

ambiguous smoke results in a flame test

suggest compounds with multiple functional groups or combined aromatic/aliphatic compound

rapid and instantaneous combustion during a flame test is

indicative of high oxygen content

combustion of sparks during the flame test is

indicative of high nitrogen content or nitro groups

yellow, smoky flame during the flame test is

indicative of aromatic, unsaturated, or high molecular weight aliphatic compounds

yellow, non smoky flame during the flame test is

indicative of lower molecular weight aliphatic organic compound

clear, blueish flame during the flame test is

indicative of oxygen-rich compounds (i.e., ethanol)

Procedure for Bellstein test for ______ or ________ _______

place coil of copper with unknown into the flame

transient green color in bellstein test is due to

copper that has been made volatile in the presence of halogenated organic compounds → positive test for halogen, indicating presence of bromine, chlorine, or iodine

What is the bellstein test not able to distinguish between?

alkyl or aryl halides → both give positive tests

what halogen is not detected by the Bellstein test?

fluorine

Procedure for the silver nitrate test

unknown + silver nitrate in ethanol → let stand for 5 mins at room temp → if no development of precipitate during this time, heat solution in water and observe any change

what halogen is not detected by the silver nitrate test

fluorine

what reaction does the silver nitrate test exhibit relative reactivities of?

SN1 reactions

during the silver nitrate test, benzylic, allylic, and tertiary alkyl halides give

an immediate precipitate at room temperature

during the silver nitrate test, primary and secondary alkyl halides give

a precipitate upon heating

during the silver nitrate test, aryl and alkenyl halides

do not react, even with heating

formation of white precipitate during the silver nitrate test is

indicative of Cl

formation of pale yellow precipitate during the silver nitrate test is

indicative of Br

formation of yellow precipitate during the silver nitrate test is

indicative of I

what functional group gives a false positive in the silver nitrate test?

carboxylic acid

how to detect the false positive of ______ ______ in a silver nitrate test

add two drops of 5% nitric acid; silver carboxylates will dissolve but silver halides will not

procedure for chromic acid test for __________

• Tube 1: unknown + reagent-grade acetone

• Tube 2: only acetone as a negative control

• To both tubes: chromic acid

• Immediately examine the color of the tubes

immediate appearance of blue-green color within 2s in a chromic acid test is

indicative of primary or secondary alcohols or aldehdyes

retention of orange color during the chromic acid test is

indicative of the presence of tertiary alcohols

what functional group gives a false positive in the chromic acid test for ALCOHOLS

• aldehydes because they can also be oxidized with chromic acid

• acetone containing trace amounts of isopropanol

procedure for the Lucas Test for __________

_______ reagent (ZnCl2 + conc. HCl) + unknown → shake 15 seconds → allow mixture to stand → observe whether there is a precipitate after 5 minutes (precipitate could be a liquid)

what does the Lucas test for ______ depend on?

How easily a carbocation intermediate forms from the alcohol

what happens to the carbocation intermediates during the Lucas test?

converted to the corresponding alkyl chloride; how fast the precipitate forms depends on structure of the ______.

positive test for _______ during the Lucas test is

the appearance of liquid precipitate or separate liquid → looking for a precipitate

formation of a precipitate in two minutes during the Lucas test for ________ is

indicative of benzylic, allylic, of tertiary alcohol (rapid SN1)

formation of a precipitate after ten minutes during a Lucas test is

indicative of a secondary alcohol (slow SN1)

formation of no precipitate during the Lucas test is

indicative of a primary alcohol (no SN1 under these conditions)

procedure for Ferric chloride test for ________

unknown + water + several drops of ferric chloride → observe color immediately

immediate production of intense red, blue, purple, or green color during a ferric chloride test is

indicative of a phenol

why do some phenols give a false negative on the ferric chloride test

steric hindrance → negative test is unreliable

what can give a false positive result on a Ferric chloride test

esters and 1,3-dicarbonyl compounds sometimes show intense coloration

procedure for bromine-water test for _______

unknown + EtOH + bromine reagent (until yellow color persists) → shake the reaction mixture after each addition → moisten litmus (pH) paper and hold at end of tube → watch for color change on litmus paper

disappearance of yellow bromine coloration during a bromine-water test is

indicative that the bromine has been consumed → this suggests that the electron0rich aromatic ring of a phenol has been brominated

The color of the litmus paper turns _____ during a positive result of the bromine-water test for ______ due to the _________ of __

pink; phenols; evolution of HBr

What species may give a false positive result during the bromine-water test?

highly activated aromatic compounds (aromatic ethers) and beta-carbonyl compounds

DNP test for ______ and _______ procedure

DNP reagent (2,4-dinitrophenylhydrazime and sulfuric acid in aqueous ethanol) + unknown + methanol → shake → observe for formation of precipitate → no ppt, heat for three minutes in water bath and cool in ice

appearance of red, orange, or yellow ppt during the DNP test is

indicative of the presence of an aldehyde of ketone

what can the color of the ppt from a DNP test tell you?

distinguishes between conjugated carbonyls (directly attached to an alkene or aromatic ring) and nonconjugated carbonyls

yellow ppt during the DNP test is

indicative of a nonconjugated carbonyl

red or orange ppt during the DNP test is

indicative of a conjugated carbonyl

procedure for chromic acid test for ______ and _______

• Tube 1: unknown + reagent-grade acetone

• Tube 2: only acetone as a negative control

• To both tubes: chromic acid

• Immediately examine the color of the tubes

appearance of a blue-green color within 2s for a chromic acid test for ______ and _______ is

indicative of aldehydes

appearance of no color change within 2 s for a chromic acid test for _______ and _________ is

indicative of ketones because they are negative on this test

what functional groups have a positive result in the chromic acid test?

primary/secondary alcohols and aldehydes

how does the chromic acid test work?

chromic acid oxidizes both primary/secondary alcohols and aldehydes to carboxylic acid

when is the only time you SHOULD use the Tollens test?

when the DNP test has already confirmed the presence of an aldehyde or ketone

how to prepare the reagent for the Tollens test:

5% AgNOs + NaOH + HH4OH → until silver ppt disappears ALMOST completely → use only the supernatant, leave the solid behind

procedure for the Tollens test

unknown + new test tube + freshly prepared ______ reagent → look for the formation of a silver mirror or black precipitate → if neither form after 10 minutes, warm tube in water bath for ten minutes and check again

formation of a silver coating inside the test tube or a black ppt of finely divided Ag metal during the Tollens test is

indicative of a positive test and the presence of an aldehyde

how does the Tollens test work?

the Ag(I) in the reagent produces Ag(0) as it oxidizes the aldehyde to a carboxylate salt

the lack of formation of a silver mirror or black precipitate during the Tollens test is

indicative of a ketone (not an aldehyde) because ketones are not oxidized under these conditions

what can cause a black ppt instead of a silver mirror during the Tollens test?

used or dirty glassware

what functional groups may give a false positive in the Tollens test?

some aromatic amines and phenols

how to prepare the reagent for the iodoform test for ______ and _________

solution of KI and I2 in water; a deep brown solution

procedure for the iodoform test for _________ and __________

unknown + tetrahydrohuran (for water-insoluble unknowns)/water (for water-soluble unknowns) + NaOH + iodoform test reagent (take note of color and volume or reagent added → with each drop of reagent added, the color should disappear → continue adding reagent until the color persists for more than 2 minutes → add NaOH to decolorize excess reagent → fill the tube with water and let it stand for 15 minutes → note the presence of absence of a yellow precipitate

yellow ppt in the iodoform test is

indicative that the unknown compound contains a methyl ketone, RCOCH3

what compounds give a false positive on the iodoform test for ______ and _________

ethanol and other alcohols with the type CH3CH(OH)R and acetaldehyde

how does the iodoform test for ______ and ________ work

disappearance of the brown color as the reagent is added is consistent with alpha-iodination of the ketone via a ketone enolate → with a methyl ketone, the reaction happens three times in successtion to afford RCOCI3 and then CHI3 (iodoform), which is released by nucleophilic acyl substitution ob RCOCI3 by OH-

iodoform

pale yellow solid with a foul odor

procedure for NaHCO3 test for ________ _______

perform the solubility test using NaHCO3 → observe if bubbles form → of no bubbles, immerse in hot water bath and examine again

formation of bubbles in the NaHCO3 test for ______ _____ is

indicative of the evolution of CO2 gas which is expected when NaHCO3 mixes with an acid that is stronger than H2CO3

basis for the NaHCO3 test for carboxylic acids

carboxylic acids (pka ~ 4) protonate HCO3- abd produce CO2, but most phenols (pka ~ 10) do not

what compounds can give a false positive in the NaHCO3 test for ______ _____

• phenols bearing strong EWGs

• liquid aldehydes that have likely been contaminated with carboxylic acid due to air oxidation

Procedure for Hinsberg test for ________

unknown + HaOH + benzenesulphonyl chloride → stopper and shake vigorously for 5-10 minutes → test with pH paper to det. if it is still basic → if not, add NaOH and shake more → separate any insoluble material → test its solubility in HCl → acidify filtrate and promote crystallization by cooling and scratching the inside of a test tube

soluble in NaOH solution and precipitates or crystallizes only after acidifying (Hinsberg test)

indicative of primary amines because they afford a secondary sulfonamide (RNHSP2Ph) with a relatively acidic N—H bond

insoluble in NaOH and fraction A is insoluble in HCl (Hinsberg test) is

indicative of secondary amines because they have no N—H bond to deprotonate

insoluble in NaOH and fraction A is soluble in HCl (Hinsberg test) is

indicative of tertiary amines, because they don’t react with PhSO2Cl and unreacted amine is insoluble in NaOH

procedure for Hydroxylamine/ferric chloride test for esters

unknown + saturated ethanolic solution of hydroxylamine hydrochloride + ethanoliic KOH → heat to boiling → acidify with HCl → add 5% solution of FeCl3 dropwise → examine color

formation of deep red or purple color (Hydroxylamine/ferric chloride test) is

indicative of the presence of an ester

Procedure for Iron (II) hydroxide test for _______ __________

unknown + freshly prepared aqueous solution of 5% iron (II) ammonium sulphate + H2SO4 + 2M ethanolic KOH → shake well → check for precipitate and examine color immediately and after 1 minute

presence of a red-brown or brown precipitate in the Iron (II) hydroxide test is

indicative of a positive test for nitro groups; the ppt may appear blue, then turn brown within 1 minute

• slight darkening of the solution or the appearance of a greenish color does NOT constitute a positive test for nitro groups