O chem lab midterm

Experiment 14 - Sodium Bisulfite Addition Complex

It provides a positive test for aldehydes and low molecular weight methyl ketones - the same data that can be derived from other tests.

SA

Monofunctional carboxylic acids with 5 carbons or fewer

Experiment 24 - Ninhydrin Test

Ninhydrin reacts with most α- and β-amino acids to produce a blue or bluish-red dye and is used in biochemical analyses to detect essential amino acids. Proline and hydroxyproline are exceptions and give a yellow color instead. Use glycine as the control.

Experiment 37 - Bromine Solution

A dilute solution of bromine in dichloromethane will be available in Hood N. Add 1-3 drops of an unknown liquid to 1 mL of the bromine solution in a test tube. A positive test is the loss of color as bromine is consumed. Solid samples must be dissolved in a minimum amount of CHCl3 and added to the test tube. Be aware that ketones, phenols, and aromatic amines may also react to discharge the bromine color, but these reactions are also accompanied by evolution of HBr (the reaction is substitution and not addition). HBr evolution can be detected by using a piece of moist blue litmus paper held over the mouth of the test tube. Use cyclohexene as a control. Positive-CLEAR

Experiment 41 - Chloroform and Aluminum Chloride

Aluminum chloride and chloroform are both available in Hood N. The generation of any color other than yellow is a positive indication for the presence of an aromatic ring of some sort. However, the specific colors given in the table on page 337 are valid only if the unknown is an aromatic hydrocarbon or an aromatic halide. Other functional groups can give misleading color changes that are unrelated to the type of aromatic nucleus. The IR spectrum is a better way to determine the presence of aromatic characteristics. Use naphthalene as a control. Positive-any color other than yellow!!!

Experiment 12 - 2,4-Dinitrophenylhydrazine Test (2,4-DNP Test)

The 2,4-DNP reagent reacts with aldehydes and ketones to give an orange or red-orange precipitate. Other carbonyl compounds such as carboxylic acid derivatives do not react generally although there are a few esters that give false positive results. Be aware that while this is among the most reliable of all qualitative tests, there are a few ketones that give liquid rather than solid 2,4-dinitrophenylhydrazones and a few highly hindered ketones that fail to react. Liquid 2,4- DNPs usually appear as insoluble red-orange oils. The 2,4-DNP precipitate from this test is a derivative, so you may want to keep it in case its melting point will be useful later

Experiment 21 - Nickel Chloride Test for Secondary Aliphatic Amines

The reagent will be located on the shelf, but the reaction must be done in a hood due to the foul odor of carbon disulfide. Use piperidine (located in Hood N) as a control.

Experiment 44 - Treatment of Aromatic Nitro Compounds with Sodium Hydroxide

This experiment detects the presence of more than one nitro group on an aromatic ring by the intense colors of the Meisenheimer complexes produced when hydroxide ion reacts with the electron-deficient nucleus. The first procedure requires 20% NaOH, which needs to be prepared immediately before use (fresh solution). The less reliable alternative procedure uses 10% NaOH which is available in Hood A. Use m-dinitrobenzene as a control.

Experiment 1 - Hydrolysis of Acid Anhydrides and Acyl Halides

This experiment is redundant and does have to be done per se since the same information is obtained by doing solubility testing in 5% sodium bicarbonate. If you have IR signals which indicate an anhydride, simply warm the test tube when you are doing the solubility test in 5% sodium bicarbonate. Bubbles of CO2 should evolve when the anhydride is converted to the acid.

Experiment 27 - Periodic Acid Oxidation of Vicinal Diols

This test is positive for a variety of vicinal oxygen functions as indicated by the equations on pages 308-9. Use ethylene glycol or glucose as a control. White precipitate!!!

Experiment 2 - Hydroxamic Acid Test

This test is used mainly to detect the presence of an ester function, but it can be modified to test for amides and nitriles. The following solutions are available on the reagent shelf to test esters: 0.5 M hydroxylamine hydrochloride in ethanol, 5% ferric chloride, 6 M NaOH, 1 M HCl, 1 M hydroxylamine ∙ HCl in propylene glycol and 1 M KOH. Use methyl benzoate as an ester control, benzamide as an amide control, and acetonitrile for a nitrile control. Most esters require a boiling time of 2 minutes in the first step of the procedure to give a strong positive test. BURGUNDY MAGENTA IS POSITIVE

Experiment 15 - Tollens Test

This test was developed for use in carbohydrate chemistry to detect reducing sugars. It is not a general test for aldehydes despite the implications in your text book. Many water-soluble aldehydes do give positive tests, but you will be better served if you limit the use of the Tollens test to carbohydrate unknowns. A more reliable method to distinguish aldehydes from ketones is the Jones Test (Experiment 8). The information about controls in your text is wrong. Acetone and benzaldehyde both give negative tests. Glucose gives a strong positive test and should be used as the control for this experiment. SILVER IS POSTITIVE TEST

N

alcohol, aldehyde, ketones, esters, ethers, epoxide, alkenes, alkynes, aromatics

B

aliphatic amine more than 8 c, aniline

Sb

amines with less than 6 carbons

S2

amino acids, amine hydrochlorides

A1

carboxylic acid with more than 6 carbons, phenols with EWG in ortho or para position

S1

monofunctional alcohols, aldehyde, ketones, esters, nitriles, amides

Experiment 20 - Nitrous Acid

nitrous acid test is not particularly useful except for 1° amines. If the 1° amine is aromatic, the diazonium salt is stable at 0 °C in an ice bath. The presence of an aromatic diazonium salt can be determined by the coupling reaction with the sodium salt of 2-naphthol, which produces a red or orange azo dye. If the 1° amine is aliphatic, the resulting diazonium salt is unstable even at 0 °C and decomposes by the vigorous evolution of N2 gas. The loss of nitrogen is usually fast enough to cause liquid to foam out of the container, so be cautious. Use p-toluidine as a control for a 1° aromatic amine and t-butylamine as a control for a 1° aliphatic amine.

A2

phenols, enols, oximes, imides, sulfonamides, thiophenols, with more than 5 carbons

I

saturated hydrocarbons, haloalkanes, aryl halides, deactivated aromatics, diaryl ethers

MN

sulfur or nitrogen

Experiment 35 - Silver Nitrate Solution (Use in conjunction with Experiment 36.)

Despite the variety of uses described in the text book for this test, in practice it is useful only as a sub-classification test for alkyl chlorides and alkyl bromides. The mechanism for the reaction is SN1 and a positive test is the formation of a precipitate of either AgCl or AgBr as the case may be. Alkyl iodides react too rapidly and cannot be differentiated easily by this test.Reaction rates are used to determine whether the alkyl halide is 1°, 2°, or 3°. Since 3°, benzylic, and allylic carbocations are the most stable, the corresponding halides react rapidly to produce the silver salt. Primary alkyl chlorides and bromides react very slowly (if at all), and aromatic halides do not react.

Experiment 28 - Benedict's Solution

Benedict's test is a sub-classification test used to detect reducing sugars. It gives exactly the same information as the Tollens test and is probably more reliable. Use glucose as a control. Positive: red green or yellow precipitate Negative: clear or a little blue

Experiment 8 - Chromic Anhydride Oxidation (Jones Test)

Jones reagent oxidizes many different types of compounds, but it is used mainly in this lab to differentiate between aldehydes and ketones. It can also serve as a sub-classification test for alcohols since 1° and 2° alcohols react but 3° alcohols do not. Be aware that the observations for a positive test are not the same for aldehydes and alcohols. Alcohols usually react within 2 to 4 seconds and produce a color change from orange to green or blue-green. Aldehydes are slower and may require 20 to 30 seconds, but the color change tends toward dark olive green rather than blue-green. Obviously, the proper control must be used depending on application. For alcohols, the control is 2-butanol; and for aldehydes, the controls are benzaldehyde and butanal. Aromatic amines and phenols also react with Jones reagent, but the result is meaningless since it is not diagnostic. Reactions with amines and phenols produce heat and an accompanying color change from orange to dark brown or black. ORANGE TO GREEN-Alcohol ORANGE TO DARK OLIVE GREEN-ALDEHYDE ORANGE- Ketone

Experiment 38 - Potassium Permanganate Solution (Baeyer Unsaturation Test)

Only the reagent for part (a) will be available. The observations for a positive test are the disappearance of the purple color and the formation of a brown precipitate. If ethanol is used as a solvent for the unknown, no observations made after 30 seconds are likely to be valid since the alcohol will oxidize slowly and give the same result as an alkene or alkyne. The text book is not correct regarding observations made after 5 minutes. Primary and secondary alcohol unknowns may give a false positive test due to oxidation of the carbinol group and should be tested for unsaturation using Experiment 37 instead. Likewise, phenols, aldehydes, aromatic amines and other compounds that are easily oxidized may react as well. Use cyclohexene as a control. Positive-BROWN ppt

Experiment 7 - Ceric Ammonium Nitrate

This is a general test for alcohols, but it can be much more useful by taking advantage of information in Table 9.3, p. 267. Almost all alcohols form an immediate red complex with the reagent, but the color disappears after a period of time that depends on the type of alcohol. Be sure to note the amount of time required for the color change from red to colorless and be awarethat CO2 may also be evolved in some cases. There are problems described on p. 266 associated with alcohol unknowns that also contain an amino group. Use glucose for the control. This test is not designed for phenols. The brown color or precipitate from the reaction of this reagent with a phenol simply tells you that an oxidation has taken place. It does not confirm a phenol. This experiment is for alcohols only. If you want to test for a phenol, use Experiment 45. RED COMPLEX POSTITIVE!!!!

Experiment 9 - Lucas Test

This is a sub-classification test for alcohols and is among the most widely misused tests in the entire course. First, if the unknown cannot be verified as an alcohol using other tests, then the Lucas test is a waste of time. Second, the unknown must be soluble in the reagent. This usually means that the compound will have no more than 6 carbon atoms in its structure. Since the observation for a positive test is the appearance of a layer or an emulsion, the test is invalid unless the unknown is soluble at first in the reagent. The controls are 1-butanol for a 1° alcohol, 2-butanol for a 2° alcohol, and t-butyl alcohol for a 3° alcohol.

Experiment 19 - Benzenesulfonyl Chloride (Hinsberg Test)

This is a sub-classification test for amines. Benzenesulfonyl chloride is located in Hood N; 10% NaOH and 10% HCl are both located in Hood A. Tertiary amines do not react, but 1° and 2° amines produce benzenesulfonamide derivatives during this test, so the precipitate should not be discarded. The benzenesulfonamide derivative of a 1° amine is soluble in 10% NaOH, so the precipitate does not form until the reaction mixture is acidified with 10% HCl in the last step of the procedure. Use aniline as a control for a 1° amine and N-methylaniline as a control for a 2° amine. It is not necessary to run a control for a 3° amine since no reaction will occur anyway.

Experiment 11 - Iodoform Test

This is a sub-classification test for methyl ketones and 2° alcohols with a methyl group on the carbinol carbon. The procedure in the book works substantially better with the following modifications. Use 2 mL of dioxane (rather than 5 mL) and 2 mL of 10% NaOH (rather than only 1 mL) and warm the test tube to 40-50 °C before adding the iodine solution. A positive test is indicated by the formation of a yellow precipitate with a characteristic odor (that is not foul, as the book states), and a MP of ~120 °C. False positive tests are not common, but they can occur. To be safe, the yellow precipitate should be isolated and recrystallized from methanol to verify its MP. This is not a waste of time since iodoform is a legitimate derivative for methyl ketones and 2° methyl carbinols. Use acetone or acetophenone for ketone controls and 2-butanol for a methyl carbinol control. False positive tests can result from using a test tube that has been dried with acetone or ethanol but is not free of solvent vapor. YELLOW PPT MP of 120

Experiment 45 - Ferric chloride-Pyridine Reagent

This is a test for enols and phenols (which are stable enols) and must be done in the hood due to the unpleasant odor of pyridine. The ferric chloride solution (1% in CHCl3) is located on the shelf, but pyridine and chloroform are in Hood N. Use phenol as a control.

Experiment 42 - Ferrous Hydroxide Reduction

This is a test for nitro groups that uses ferrous ion as a reducing agent. It is not necessary to remove air with a flow of inert gas as described in the text book. Nitrobenzene gives a strong positive test and should be used as a control and tested side-by-side with your unknown. Even a small deviation in the red-brown color of the ferric hydroxide precipitate between the control and your unknown is important and should probably be interpreted as inconclusive.

Experiment 36 - Sodium Iodide in Acetone Test (Use in conjunction with Experiment 35.)

This is also a sub-classification test for alkyl chlorides and bromides, but the mechanism is SN2 rather than SN1. A positive test is the formation of a precipitate of either NaCl or NaBr as the case may be. The order of reactivity for halides parallels the rates of reaction for 1°, 2°, and 3° substrates in SN2 reactions; i.e. 1° > 2° > 3°. The same controls are used as in Experiment 35. This test is invalid for alkyl iodides. The most common error occurs when the solution is heated, which can lead to loss of the acetone solvent. If too much solvent is lost, then the NaI will precipitate and give the appearance of a positive test.

Experiment 31 - Sodium Bicarbonate Test

This is nothing more than a modification of the solubility test in 5% NaHCO3, which has likely already been done. Simply knowing that the unknown dissolves in both 5% NaOH and 5% NaHCO3 is sufficient to classify the unknown as a strong acid. However, this test can be useful if the acid reacts so slowly that the evolution of CO2 is not readily observed. The use of a methanol solution of the acid in this test rather than the solid acid speeds the reaction and may cause the evolution of CO2 to be more easily detected.

Experiment 26 - Borax Test

This test detects 1,2-diols, vicinal polyols, and carbohydrates but is not totally reliable. A negative test should be confirmed by performing Experiment 27 as well. Use sucrose or ethylene glycol as a control. warm pink, cool clear

Experiment 22 - Nickel Chloride/Nitrosalicylaldehyde Test for Primary Amines

This test for primary amines is fairly reliable but is prone to give inconclusive results that usually appear as a faint turbidity rather than a large amount of heavy precipitate. Use aniline as a control. A small amount of precipitate may be positive but is probably not to be trusted.

Experiment 18 - Sodium Hydroxide Hydrolysis of Amides and Nitriles

This test is nothing but a simple basic hydrolysis of an acid derivative using boiling 10% NaOH, but it is also very useful. Both nitriles and 1° amides hydrolyze under basic conditions to produce ammonia, which can be detected by odor or by its reaction with moist red litmus paper. However, the test can be misleading unless the amide is primary. Secondary and tertiary amides will give a positive test only if the resulting amine product is sufficiently volatile to escape from the boiling hydroxide solution. Generally, this means the amine must have a boiling point below 80 °C. Thus, acetanilide will give a negative test. The 10% NaOH solution is available in Hood A, and either benzamide or acetonitrile may be used as a control.