Question

post lab:experiment 19 a.) benzaldehyde and acetophenon

Post-Lab: Experiment 19 1. Explain how you could use the simple laboratory tests performed in this experiment to distinguish between the following compounds. a. Benzaldehyde and acetophenone b. 2-Pentanone and 3-pentanone c. Acetaldehyde and propionaldehyde d. 3-Pentanone and pentanal 2. Only one aldehyde and only one primary alcohol give a positive iodoform test. What are the structures?

I need help with A-D and #2 please

Answer 1

Answering 2 first ----

Ethanal or Acetaldehyde is the only aldehyde which gives a positive iodoform test.

Structure for ethanal (C2H4O)

H-

The only primary alcohol which gives a positive iodoforn test is Ethanol

Structure for ethanol (C2H5OH)

Η Η Η – 0 – 2 – 3 – Η Η Η

Coming to the first question

1. a Tollen's test will distiguish benzaldehyde and acetophenone

Aldehydes respond to Tollen's test, Benzaldehyde being and aldehyde reduces Tollen's reagent to a red-brown precipitate of Cu2O, but Acetophenone being a ketone doesn't.

cao Cursos cances de coco CHECHO + 2Ag (NH3)2 + 3OH- CH3COO + Ag+ 4NH3 + 2H2O Benzaldehyde Tollen's reagent Benzoate ion Silver mirror

They can also be distinguished using Iodoform test

Acetophenone being a methyl ketone undergoes oxidation by sodium hypoiodite(NaOI) to give a yellow precipitate of Iodoform But Benzaldehyde doesn't respond to this.

CH:COCHz + 3NaOI – Acetophenone CH3COONa + CHI3 + 2 NaOH Sodium benzoate lodoform (yellow ppt)

1. b Iodoform test can distinguish between 2-pentanone and 3-pentanone

2-pentanone being a methyl ketone reacts to the test and gives yellow precipitate whereas 3-pentanone doesn't respond to the test.

CH3CH2CH2-C- CH + 3 NaOI Pentan-2-one CH CH CH.COONa + CHI + 2NaOH Sodium butanoate lodoform (yellow ppt) No yellow ppt of iodoform CH:CH -- CH CH3 + NaOl- Pentan-3-one

1. c Iodoform test can distinguish acetaldehyde and propionaldehyde

Acetaldehyde having one methyl group linked to the carbonyl atom reacts to this giving yellow precipitate but propionaldehyde doesn't react as it doesn't have any methyl group linked to the carbonyl atom.

CHỊCHO + 3NaOI Ethanal HCOONa+ CHI3 + 2 NaOH Sodium lodoform methanoate (yellow ppt)

1. d Tollen's reagent test can distinguish 3-pentanone and pentanal

Pentanal on reacting with Tollen's reagent will give silver precipitate but 3-pentanone won't .

R-CHO + [Ag(NH3)2]OH – Ag +R-COO-NH4+ +H20 +NH3

Here is the Tollen's reagent.

[Ag(NH3)2]OH