Waite conclusicn 78 on uhy Cmpes geaocted on uwhy Cmpds Reoctecl Data: Make obse

Question

Waite conclusicn 78 on uhy Cmpes geaocted on uwhy Cmpds Reoctecl Data: Make observations for each of the following sets of tests. 1. Classification Test: 2,4-Dinitrophenylhydrazine (see page 73) the wasy they clac Rece wthey dacl (Note: use about 0.2 mL of liquid sample) Determine if a positive test is obtained with each of the following compounds. Do not solate crystals or take melting points. Record your observations. Organic waste container. Waste in the Qual Rent cCyclohexanone 2· Classification Test: Chromie Acid (Croy-H,so-acetone) (page 71) onduct this test and determine if a color change occurs with each of the following -biutone compounds. Record your observations. Waste in the Chromic Acid Waste container. 10 Benzaldehyde danh baa a negahse %2-Pentanone der red-aangei negative 3. Classification Test: lodoform Test (I-KI-NaOH) (page 72) Conduct this test with each of the following compounds. Record your observations. ellouco 2-pentanone cyclohexanone Cleah e cycloh ear,--na tot anat -ositive

Explanation / Answer

Classification Test of 2,4-Dinitrophenylhydrazine :

1) 2 Butanol : No precipitate (negative test)

2) Benzaldehyde : yellow to orange precipitates (positive test)

3) Cyclohexanone : yellow to orange precipitates (positive test)

2,4-Dinitrophenylhydrazine can be used to qualitatively detect the carbonyl functionality of a ketone or aldehyde functional group. A positive test is signaled by a yellow, orange or red precipitate (known as a dinitrophenylhydrazone.) If the carbonyl compound is aromatic, then the precipitate will be red; if aliphatic, then the precipitate will have a more yellow color.The reaction between 2,4-Dinitrophenylhydrazine and a ketone is shown below:

RR'C=O + C6H3(NO2)2NHNH2 C6H3(NO2)2NHNCRR' + H2O

This reaction can be described as a condensation reaction, with two molecules joining together with loss of water. It is also considered an addition-elimination reaction: nucleophilic addition of the -NH2 group to the C=O carbonyl group, followed by the removal of a H2O molecule.

Chromic Acid Test of CrO3-H2So4-acetone :

1) 2 Butanol : blue to green precipitate (positive test)

2) Benzaldehyde : no precipitates (negative test)

3)2 pentanone : no precipitates (negative test)

The Jones Oxidation allows a relatively inexpensive conversion of secondary alcohols to ketones and of most primary alcohols to carboxylic acids. Benzaldehyde and 2 pentanone does not nhave alcohol functional group so they did not react with jones reagent.on other hand 2 butanol is secondary alcohol which react with jones reagent and form corresponding ketone i.e. 2 butanone

Iodoform Test of I2-KI-NaOH :

1) 2 Butanol : yellow precipitate (positive test)

2) 2 pentanone : yellow precipitates (negative test)

3) cyclohexanone : no precipitates (negative test)

When iodine and sodium hydroxide are used as the reagents, a positive reaction gives iodoform. Iodoform (CHI3) is a pale-yellow substance.

The net reaction starting from a methyl ketone and hypohalite may be written:

R-CO-CH3 + 3XO- ==> RCOO- + CHX3 + 2OH-

The oxidation of alcohol to a ketone may be written:

R-CHOH-CH3 + XO- ==> R-CO-CH3 + X- + H2O

The net reaction starting from alcohol and hypohalite is therefore:

R-CHOH-CH3 + 4XO- ==> RCOO- + CHX3 + X- + H2O + 2OH-

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