Orgo Lab Exam
Aryl Halide
Halogen attached directly to an aromatic ring
Alkyl halide
AKA haloalkane
Tollens Test
Aldehyde test Mix fresh Tollens reagent w/ unknown. Warm for up to 10m The formation of Ag metal coating (silver mirror) inside the test tube, or a black ppt of finely divided Ag metal, constitutes a positive test, indicating the presence of an aldehyde. The Ag(I) in the reagent produces Ag(0) as it oxidizes the aldehyde to a carboxylate salt. Ketones are not oxidized under these conditions and give a negative test. Used or dirty test tubes may result in a black precipitate instead of the silver mirror. Some aromatic amines and phenols give a false positive in this test. Liquid aldehydes are likely to be contaminated by carboxylic acids due to air oxidation; a distilled sample of such aldehydes may give more reliable results in the Tollens test.
Bromine/CCL4 Test
Alkene Test Positive-Solution becomes clear (looses bromine color) Must be observed immediately as Br will evaporate
Silver Nitrate Test
Alkyl Halides Test Add Silver Nitrate, Precipitate is positive test Benzylic, Allylic, and Tertiary tertiary alkyl halides give immediate + Primary and Secondary Alkyl Halides give + when heated Aryl and alkenyl halides do not react, even with heating White ppt = Cl; pale yellow ppt =Br, yellow ppt = I. Carboxylic acids may give a false positive, a precipitate which is the silver carboxylate salt (RCO2Ag). To detect this false positive, add two drops of 5% nitric acid; silver carboxylates will dissolve but silver halides will not.
Belstien Test
Alkyl or Aryl Halides Test (B) Positive Burning sample on copper wire, green flames or sparks around copper as it is volatized Indicates Cl Br I but not F
Flame Test
Aromatic Test Nature of combustion: Rapid and instantaneous combustion -- high oxygen content Explosive (sparks) -- high nitrogen content, or nitro groups Color of the flame: Yellow smoky flame -- aromatic, unsaturated, or high MW aliphatic compounds Yellow non-smoky flame -- lower MW aliphatic organic compounds Clear bluish flame -- oxygen-rich compounds (ethanol):
Allylic
On the carbon adjacent to a double bond
Benzyl vs Phenyl
Phenyl attached directly to ring
Lucas Test
Test for Alcohol (not primary) Lucas Reagent: ZnCl2 and HCl Mix and shake, wait 5m, Precipitate=+ 2 minutes -- benzylic, allylic, or tertiary alcohol 10 minutes -- secondary alcohol No ppt -- primary alcohol
2,4-Dinitrophenylhydrazine (DNP) Test
Test for Aldehyde/Ketone Mix reagent and shake, wait for precipitate. If none, boil and ice bath Precipitate=Positive The appearance of a red, orange, or yellow precipitate indicates the presence of an aldehyde or ketone. The color of the precipitate can distinguish conjugated carbonyls (directly attached to alkene or aromatic ring) from non-conjugated carbonyls; a yellow ppt indicates the carbonyl is nonconjugated, while orange or red ppt indicates conjugation. Positive or negative for precipitate is the strongest evidence from this test; the color can sometimes be misleading.
Hinsberg Test
Test for Amines Combine 0.2 mL of liquid unknown (or 0.2 g of solid unknown) with 5 mL 10% NaOH solution. Add 0.4 mL benzenesulfonyl chloride. Stopper the tube and shake vigorously for 5-10 min, cooling in a water bath if it becomes hot. Test the solution with pH paper to see if it is still basic. If not, add another 1 mL 10% NaOH and shake for 5 min. Separate any insoluble material ("Fraction A", may be liquid or solid) by decanting or filtering and test its solubility in 5% HCl. Acidify the filtrate ("Fraction B") by dropwise addition of concentrated HCl (check with pH paper) and promote crystallization by cooling and scratching the inside of the test tube. Primary amines afford a secondary sulfonamide (RNHSO2Ph) with relatively acidic N- H bond; it is therefore soluble in NaOH solution and will precipitate or crystallize only after acidifying "Fraction B". Secondary amines afford a tertiary sulfonamide (R2NSO2Ph) which has no N-H to deprotonate, so it will be insoluble in NaOH solution and detected as "Fraction A", insoluble in 5% HCl. Tertiary amines will not react with PhSO2Cl, and the unreacted amine should be insoluble in NaOH, so it will be detected as a "Fraction A" which is soluble in 5% HCl. Some secondary amines react slowly, and may require warming of the reaction mixture. Use the Hinsberg test only after establishing with some certainty that the unknown is an amine.
Sodium BiCarbonate Test
Test for Carboxylic Acid Add Sodium Bicarbonate, look for bubbles Bubbles=+ The formation of bubbles suggests the evolution of CO2 gas. This is expected when NaHCO3 is mixed with an acid stronger than H2CO3. In such cases the HCO3 - ion is protonated to make H2CO3, which then decomposes to afford H2O and CO2. Carboxylic acids (pKa of about 4) protonate the HCO3 - ion and produce CO2, but most phenols (pKa of about 10) do not. However, phenols bearing strongly electron-withdrawing groups may give a false positive. Liquid aldehydes are likely to be contaminated by carboxylic acids due to air oxidation, and may give a false positive. If other evidence suggests an aldehyde, then a false positive here can be ruled out by repeating the test on a distilled sample of the unknown.
Hydroxyl Amine/Ferric Chloride
Test for Esters To 2-3 drops or ca. 50 mg unknown add 10 drops of a saturated ethanolic solution of hydroxylamine hydrochloride and 10 drops of 20% ethanolic KOH. Heat the mixture to boiling, acidify with 5% HCl, then add a 5% solution of FeCl3 dropwise. Examine the color. Formation of a deep red or purple coloration (a positive result) suggests the presence of an ester. Do this test only if the compound is insoluble in NaOH, as phenols and carboxylic acids will give a false positive. If a positive result is observed, repeat the test without using hydroxylamine hydrochloride, positive in this case indicates a phenol, not an ester
Iron(II) Hydroxide Test
Test for Nitro groups Add 2-3 drops or ca. 50 mg unknown to 2 mL of freshly prepared aqueous solution of 5% iron(II) ammonium sulfate. Add 3 drops 1M H2SO4, followed by 1 mL of 2M ethanolic KOH. Stopper the tube and shake well. Check for a precipitate and examine its color immediately, and also after 1 min. The presence of a red-brown or brown precipitate within 1 minute constitutes a positive test for nitro groups. The precipitate may initially appear blue, then turn brown within 1 min. A slight darkening of the solution or appearance of a greenish color does not constitute a positive test.
Bromine-Water Test
Test for Phenol Add Br reagent until yellow If yellow color fades=Positive The disappearance of the yellow bromine coloration is indicative of the consumption of bromine, and this suggests that a bromination of the electron-rich aromatic ring of a phenol. The color of the litmus paper turns pink in a positive test due to the evolution of HBr. A precipitate may form in some cases, and on larger scale this could be a useful derivative. Other highly activated aromatic compounds, aromatic ethers for example, could also give a positive result.
Ferric Chloride Test
Test for Phenol Mix Ferric Chloride with unknown Most phenols produce an intense red, blue, purple, or green color. Some colors are transient and must be viewed immediately upon mixing. Some phenols, especially sterically hindered ones, do not give a positive test, so a negative test is unreliable evidence. Esters and 1,3-dicarbonyl compounds sometimes also show intense coloration (false positive).
Iodoform Test
Test for methyl ketone Mix reagent (KI +I2) and unknown until consistently brown.Fill with water wait 15 mins Pale yellow precipitate = + Ethanol and other alcohols of the type CH3CH(OH)R will give a false positive, as they are oxidized to methyl ketones under the reaction conditions. Acetaldehyde also gives a positive result. : Formation of a pale yellow ppt indicates that the unknown contains a methyl ketone, RCOCH3. Disappearance of the brown coloration as the reagent is added is consistent with the alphaiodination of the ketone via a ketone enolate. With a methyl ketone, this reaction happens three times in succession to afford RCOCI3, then CHI3 (iodoform) is released by nucleophilic acyl substitution of RCOCI3 by OH- . Iodoform is a pale yellow solid (mp 119°C) with a foul odor.
Chromic Acid Test
Tests for Alcohol (1 or 2) OR ALDEHYDE Add Chromic acid: Immediate Blue/Green=+ Acetone (or aldehydes) may give false positive