Jones (Chromic Acid) Oxidation Test for Aldehydes

Standards
Cyclohexanone and Benzaldehyde

Procedure
Dissolve 10 mg or 2 drops of the unknown in 1 mL of pure acetone in a test tube and add to the solution 1 small drop of Jones reagent (chronic acid in sulfuric acid). A positive test is marked by the formation of a green color within 5 seconds upon addition of the orange-yellow reagent to a primary or secondary alcohol. Aldehydes also give a positive test, but tertiary alcohols do not.
The Jones reagent will already be prepared for you.

Positive Test
A positive test for aldehydes and primary or secondary alcohols consists in the production of an opaque suspension with a green to blue color. Tertiary alcohols give no visible reaction within 2 seconds, the solution remaining orange in color. Disregard any changes after 15 seconds.

Complications

Aldehydes are better characterized in other ways. The color usually develops in 5-15 seconds.
Cleaning up
Place the test solution in the appropriate waste container.

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Tollen’s Test for Aldehydes

Standards
Cyclohexanone and Benzaldehyde

Procedure
Add one drop or a few crystals of unknown to 1 mL of the freshly prepared Tollens reagent. Gentle heating can be employed if no reaction is immediately observed.
Tollens reagent: Into a test tube which has been cleaned with 3M sodium hydroxide, place 2 mL of 0.2 M silver nitrate solution, and add a drop of 3M sodium hydroxide. Add 2.8% ammonia solution, drop by drop, with constant shaking, until almost all of the precipitate of silver oxide dissolves. Don't use more than 3 mL of ammonia. Then dilute the entire solution to a final volume of 10 mL with water.

Positive Test
Formation of silver mirror or a black precipitate is a positive test.

Complications

The test tube must be clean and oil-free if a silver mirror is to be observed.
Easily oxidized compounds give a positive test. For example: aromatic amine and some phenols.
Cleaning up
Place all solutions used in this experiment in an appropriate waste container.

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2,4-DNP Test for Aldehydes and Ketones

2,4-DNP Test for Aldehydes and Ketones

Aldehyde or Ketone

Standards
Cyclohexanone, Benzophenone, and Benzaldehyde

Procedure
Add a solution of 1 or 2 drops or 30 mg of unknown in 2 mL of 95% ethanol to 3 mL of 2,4-dinitrophenylhydrazine reagent. Shake vigorously, and, if no precipitate forms immediately, allow the solution to stand for 15 minutes.
The 2,4-dinitrophenylhydrazine reagent will already be prepared for you.

Positive test
Formation of a precipitate is a positive test.

Complications

Some ketones give oils which will not solidify.
Some allylic alcohols are oxidized by the reagent to aldehydes and give a positive test.
Some alcohols, if not purified, may contain aldehyde or ketone impurities.

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Qualitative Analysis of Organic Compounds - Physical Constants, Preliminary Test, Solubility Tests

Qualitative Analysis of Organic Compounds

The analysis and identification of unknown organic compounds constitutes a very important aspect of experimental organic chemistry. There is no definite set procedure that can be applied overall to organic qualitative analysis. Sundry books have different approaches, but a systematic approach based on the scheme given below will give satisfactory results. Qualitative tests that require substantial quantities of a number of (often hazardous) chemicals to be stocked in the lab for experimental use are frequently being phased out of organic chemistry in favor of modern spectroscopic techniques. In order to deduce the identity of your two unknowns, you will combine one qualitative test, that for the classification of halides, with modern analytical techniques of infrared spectroscopy (IR) and mass spectrometry (MS). An elaboration on qualitative tests can be found in this Appendix and Hornback on page 291.

General Scheme of Analysis

A. Preliminary Test
Note physical characteristics: solid, liquid, color, and odor. Compounds that are yellow to red in color are often highly conjugated. Amines often have a fish-like odor, while esters usually have a pleasant fruity or floral smell. Acids have a sharp, biting odor. Odors can illicit information about your unknown; it is wise to sniff them with caution. Some compounds can have corrosive vapors or make you feel nauseous.

B. Physical Constants
Determine the boiling point or melting point. Distillation is recommended in case of liquids. It serves the dual purpose of determining the boiling point as well as purifying the liquid for subsequent tests.

C. Solubility Tests
The solubility of the unknown in the following reagents provides very useful information. In general, about 1 mL of the solvent is used with approximately 0.1 g or 0.2 mL (2-3 drops) of the unknown compound. Assistance in analyzing the results from your solubility tests can be found in the solubility flowchart given in Fieser and Williamson on page 606. (Careful, this flowchart is much more complex than our lab requires and often can make it more difficult to form conclusions from your solubility data..)

D. Group Classification Tests
After analysis of the previous tests and the compound's IR spectrum, if needed, further information can be deduced by performing carefully selected functional group classification tests.

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ORGANOCHLORINES (OCs) - structures, synthesis, properties DDD, DDE, DDT synthesis, Dicofol, Lindane

Commonly used in the past but many have been removed from the market due to their health and environmental effect and their persistence. (ex: DDT, Lindane)

DDT

Dichloro-Diphenyl-Trichloro ethane

1st modern pesticide and one of the best known synthetic pesticides. It was developed early in the world war II & initially used to combat mosquitoes spreading malaria, & other insect born human diseases among both military & civilian population & as an agricultural insecticide.
Paul Mϋller was awarded the Nobel prize in Medicine in 1948 for discovery of DDT.
Systematic name 4, 4’ –(2,2,2-trichloroethane-1,1-diyl) bis(chlorobenzene)


Chemical formula C14H9Cl5
Molecular mass 354.49g/mol
Density 1.6g/cm3
Melting point 106.5oC
Boiling point 260oC


DDT synthesis

OTHER RELATED COMPOUNDS

DDE C14H8Cl4 1,1-dichloro-2,2-bis(chlorophenyl) ethane

 

DDD 1,1-Dichloro-2,2-bis(p-chlorophenyl) ethane

Dicofol
C14H9Cl5O
2,2,2-trichloro-1,-bis(4-chlorophenyle)ethanol

Lindane
C6H6Cl6
Molecular Mass 290.83g/mol
Used as a wood preservative,
as a veterinary medicine in
Agriculture.
Lindane produces histopathalogical changes in the liver.

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INSECTICIDES - Mechanism of action, Structure, Biochemical action

Insecticides can be classified according to
– Mode of action
– Structure
– Biochemical action

MODE OF ACTION

Systemic insecticides

The chemical enters the plant either by the roots or leaves and they travel through the xylem or phloem and kill the insect feeding on it.

Fumigants

These are compounds with high vapor pressure. They enter the insect through the respiratory system.

Contact insecticides

Chemical is deposited on the surface of the plant and the insect is killed when it comes in contact with the deposited insecticide. They usually penetrate the cuticle of the insect.

STRUCTURE

Botanical insecticides
Azadirachitin from neem

Microorganisms
Bacillus thurengiensis

Insect derived
Natural pheramones, Growth regulators, Juvenile hormones

Synthetic insecticides

• Inorganic insecticides: arsenates, Fluorides, Borates, Cu(CH3CO2)2 , Cu(AsO2)2 NaF , Na2SiF6
• Organic insecticides - Organochlorines, Organophosphates, Carbamates, Pyrethroids, Synthetic pheromones
• Organometallic insecticides - Tin, Mercury compounds

BIOCHEMICAL ACTION

1) Insecticides can act on the following target sites within the nervous system.
a) Nicotine cholinergic receptor: Nocotine

b) Octopamine receptor: Amitraz

 c) Sodium channels: DDT, Pyrethroids

 d) Acetylcholinesterase: Organophosphates, Carbamates

e) Chloride ion channels: Chlorocyclodienes, Avermectins

2) Inhibitors of oxidative phosphorylation.
    Rotenone, Pyrimidifen, Diafenthiuron

3) Muscle contraction: Ryanodine

4) Growth regulators
    a) Chitin biosynthesis: diflubenzuron
    b) Juvenile hormone: methoprene
    c) Sex pheromone: gossyplure

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