Compound A is a clear colorless liquid with a familiar, pleasant odor, which boils at 91-92C. A dissolves readily in water. When a solution of 5 drops of A in 1 mL of water is tested with blue and red litmus, neither test paper is seen to change color.
The addition of a few drops of chromic acid reagent to A produces a distinct blue-green color. Heat is evolved.
When A is mixed with water and sodium hydroxide solution, then treated with several drops of solution of I2 in aquous KI, a bulky yellow precipatate is formed. The ppt. is collected, washed with water and dried. It melts at 118-122C.
A is mixed with an equal volume of 3,5-dinitrobenzoyl chloride and heated briefly. After cooling, some 5% aqueous NaHCO3 solution is added to the reaction, and a ppt. forms. collection, wahsing of the ppt. and recrystallization from ethanol/water results in colorless crystals that melt at 75-74C
~ Identify A and describe an appropriate derivative
~ Provide equations for all reactions described.
Please help.
Jay,
I'm not an organic chemist so you should confirm the following.
The boiling point has given me trouble and I may not have identified the material correctly but I can give some tips on how to make sure. First, the KI-I2 test is the classic iodoform test. The yellow bulky pptd material is CHI3, iodoform. The meltint point for iodoform, according to the Merck Index is 122. The iodoform test is a test primarily for aldehydes, ketones, and alcohols. The chromic acid simply oxidizes the material. Isopropyl methyl ketone is the only ketone listed in my tables even close (94 degrees) to the boiling point of the compound (91-92 degrees) and I don't know that it would react with 3,5-dinitrobenzoyl chloride. The only aldehyde listed is isovaleraldehyde (92 degrees C). which according to The Merck Index, has a pungent odor which violates the first part of the statement AND I don't know that it will react with 3,5-dinitrobenzoyl chloride. That leaves us with alcohols for they can be oxidized to produce the characteristic iodoform test. There is an alcohol, n-propyl alcohol, which has a boiling point of 97 degrees C (too high according to the above), AND it produces a 3,5-dinitrobenoate that melts at 74 degrees and that agrees with the statement. I don't know if this is an unknown in the lab or a problem you have been given. If a lab unknown, perhaps the boiling point above is a typo OR perhaps you measured the boiling point incorrectly OR perhaps it was a slightly impure sample. No matter which case we have, the proper thing to do is to make the alpha-naphthylurethan (melting point of 80 C) or the phenylurethan (melting point of 51 C)(which also answers the last part of the statement). That will tell you if you are on the wrong track or the right track. I hope this helps.
Based on the given information, the compound A can be identified as n-propyl alcohol.
To confirm this, you can perform the following reactions:
1. Reaction with chromic acid reagent:
A few drops of chromic acid reagent are added to compound A. This reaction will produce a distinct blue-green color, indicating the presence of an alcohol. Heat is evolved in this reaction.
2. Reaction with water and sodium hydroxide solution, followed by I2 in aqueous KI:
Compound A is mixed with water and sodium hydroxide solution. Then, several drops of a solution of I2 in aqueous KI are added. This reaction will result in the formation of a bulky yellow precipitate, known as iodoform (CHI3). The precipitate is collected, washed with water, and dried. The iodoform will melt at 118-122°C.
3. Reaction with 3,5-dinitrobenzoyl chloride:
Compound A is mixed with an equal volume of 3,5-dinitrobenzoyl chloride and heated briefly. After cooling, some 5% aqueous NaHCO3 solution is added to the reaction, and a precipitate forms. The precipitate is collected, washed, and then recrystallized from ethanol/water. This will result in the formation of colorless crystals that melt at 75-74°C.
To summarize the reactions:
1. Reaction with chromic acid reagent:
A + chromic acid → Blue-green color + heat evolved
2. Reaction with water, sodium hydroxide, and I2 in aqueous KI:
A + NaOH → A-OH + H2O
A-OH + I2 in aqueous KI → CHI3 (Iodoform) + other products
3. Reaction with 3,5-dinitrobenzoyl chloride:
A + 3,5-dinitrobenzoyl chloride → Precipitate
Precipitate + 5% aqueous NaHCO3 → Formation of ppt.
Ppt. recrystallized from ethanol/water → Colorless crystals with a melting point of 75-74°C
To verify the identity of the compound, it is recommended to perform a derivative formation using alpha-naphthylurethane or phenylurethane, which will help confirm the presence of a primary alcohol and provide the melting point mentioned in the statement (80°C for alpha-naphthylurethane or 51°C for phenylurethane).