CHEM 31.1 ORGANIC CHEMISTRY

AMINES

2009-37564

2-BSB

Abstract

Amines are organic compounds which are relative with ammonia; they are polar

basic and are miscible with water if it contains a smaller chain (Morrison & Boyd,

1992). There are three classifications of ammonia: primary, secondary and tertiary.

In order to distinguish which class does aniline, N,n-Dimethylaniline and

Diethylamine belongs to, Hinsberg test was conducted. Primary amine dissolves in

base and precipitates with reaction to acid. Secondary amine precipitates from base

and does not react with acid while tertiary amine precipitates in reaction with bases

and dissolves in acid (Glagovich, 2007). From the experiment, it was determined that

aniline is a primary amine, diethyamine is a secondary amine and N,n-dimethylaniline

is a tertiary amine.

Introduction

Amines are basic organic compounds which has the general formula of RNH2, R2NH, or R3N,

where R symbolizes an alkyl or aryl group. Amines are nearly relatives with NH3, since like ammonia

amines are polar, except for tertiary amines. In addition to their polarity, amines have higher boiling

points than non-polar compounds but have lower boiling point compared to alcohols or carboxylic acid.

(Morrison & Boyd, 1992) Since amines are polar compounds, most of it can form hydrogen bond with

water and itself, especially for small amines and except for tertiary amines; however this solubility

decreases as the hydrocarbon chain increases (Clark, 2004).

There are three classifications of amines according to the number of groups attached to the

nitrogen atom: primary (RNH2), secondary (R2NH) and tertiary (R3N). Like ammonia, this functional group

is also considered as a base due to the presence of a lone pair on nitrogen; however its association with

an aromatic ring weakens its basicity due to the delocalized lone pair in the pi system of benzene (Hunt,

n.d.). This lone pair also gives amine its nucleophilic ability in able for it achieve stability (Chemistry of

Amines, n.d.). In order to classify the given compounds into what type of amines they belong to,

Hinsberg test was conducted. Primary amine dissolves in base and precipitates with reaction to acid.

Secondary amine precipitates from base and does not react with acid while tertiary amine precipitates

in reaction with bases and dissolves in acid (Glagovich, 2007). Figure 1 shows the mechanism of

Hinsberg test.

Figure 1. The mechanism reaction of Hinsberg Test.

Objectives

The experiment on Amines aimed to achieve the following objectives:

1. To determine the physical properties of amines

2. To classify amines into their three classes: primary, secondary and tertiary

3. To study how the structures of amines affect their chemical properties.

Methodology

The experiment was based on the Chemistry 31.1 Organic Chemistry laboratory manual of the

University of the Philippines in Mindanao with reference to Organic Experiments by Fieser and

Williamson and Experimental Organic Chemistry by Most. There were no modifications done during the

experiment proper.

Presentation of Results

Table 1. Physical Property of Amines

COMPOUND SOLUBILITY IN WATER LITMUS TEST ADDITION OF CONC. HClAniline Not soluble Acidic Presence of gas which made the

compound miscible with the reagentN,N-Dimethylaniline Not soluble Acidic Smoke was emitted but the

compound remained immiscibleDiethylamine Soluble Basic The smoke emitted remained

contained in the tube on top of the compound

Table 2. Chemical Property of Amines and their Classification

HINSBERG TEST Aniline N,N-Dimethylaniline Diethylamine AFTER ADDITION OF BENZENE SULFONYL

CHLORIDE

Milky, heterogenous appearance of liquid

Presence of green substance and the liquid appears in 2

phases

Milky, homogenous appearance of liquid

AFTER ADDITON OF CONC. HCl

Presence of crystals Formation of gel-like substance

Formation of milky gel-like substance

AFTER WARMING WITH 10% NaOH

Soluble Immiscible with blue color of solution

immiscible

AMINE CLASSIFICATION Primary Tertiary SecondaryDiscussion of Results

Given the idea that the given test compounds, which were Aniline, N,N-Dimethylaniline and

Diethylamine, are amines the experiment aimed to classify into what class of amines each of the

compounds belongs to. Before classifying the compounds their physical properties were first observed.

According to Morrison and Boyd, smaller amines are miscible in water due to their short hydrocarbon

chain and because of the hydrogen molecule present in their structure. However the experimental result

showed that aniline is not miscible with water. Amines are bases, as stated on the introduction, due to

the lone pair present on nitrogen however basicity decreases when it is associated with an aromatic

ring. Aniline and N,N-Dimethylaniline resulted to an acidic pH due to its association with a benzene ring

while Diethylamine turned red litmus paper to blue indicating its basicity.

Hinsberg test was conducted to classify amines into primary, secondary and tertiary amines. It

was observed that Aniline became turbid after adding benzene sulfonyl chloride, then precipitated with

the addition of HCl and lastly became soluble after the addition of NaOH. On the other hand, N,N-

Dimethyllaniline turned to a green heterogenous solution after the addition of benzene sulfonyl

chloride, then formed a green gel-like substance after the addition of HCl and with the addition of NaOH

the solution was still immiscible and turned to blue. Lastly, Diethylamine turned to a milky homogenous

solution that when added with HCl remained unaffected and when added with NaOH the liquid is still

immiscible.

Conclusion

In conclusion, amines are polar compounds which can form hydrogen bonds with water due to

the presence of hydrogen molecule in its structure. However, their solubility with HCl varies since aniline

and diethylamine became soluble with the formation of smoke while N,N-Dimethylamine remained

immiscible. They are considered as bases due to the presence of lone pair present in nitrogen, this was

exhibited by Diethylamine, and however this basicity decreases in the presence of an aromatic ring thus

making the compound more acidic, this is exhibited by Aniline and N,N-Dimethylamine.

Amines are classified into primary, secondary and tertiary amines and this can be determined by

doing the Hinsberg test. Primary amine dissolves in base and precipitates with reaction to acid.

Secondary amine precipitates from base and does not react with acid while tertiary amine precipitates

in reaction with bases and dissolves in acid (Glagovich, 2007).

Based from the given results, Aniline is a primary amine, while Diethylamine is a secondary

amine and lastly N,N-Dimethylaniline is a tertiary amine.

Questions and Answers

1. Using structures explain the solubility of amines in water.

2. Using equations:a. Write the reaction of diethylamine with HCl, then followed by the treatment of NaOH to

the product formed.

b. Show the reaction of Hinsberg test to each test compound.Aniline:

OH- NaOH H+

C6H5NH2 + C6H5SO2Cl [C6H5SO2NHC6H5] C6H5SO2NC6H5-Na+ C6H5SO2NHC6H5

Diethylamine: OH- NaOH or H+

CH3CH2NHCH2CH3 + C6H5SO2Cl [C6H5SO2NH(CH3CH2)2] No reaction

N,N-Dimethylaniline:

OH- NaOH C6H5N(CH3)2 + C6 H5SO2Cl [C6H5SO2(CH3)2 NC6H5] C6H5SO2(CH3)2 NC6H5Na+

c. Which of the sulfonamides was soluble in alkali and why?Aniline was soluble in alkali due to the formation of salt during the reaction of aniline and concentrated HCl. The production of salt led to the solubility of aniline to NaOH to produce a clear liquid.

Literature Cited

Chemistry of Amines. (n.d.). Retrieved September 25, 2010, from http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/amine1.htm

Clark, J. (2004). INTRODUCING AMINES. Retrieved September 25, 2010, from Understanding Chemistry: http://www.chemguide.co.uk/organicprops/amines/background.html

Fieser, L., & Williamson, K. (1992). Organic Experiments. Lexington, Mass.: D.C. Heath.

Glagovich, N. (2007, July 19). Hinsberg Test. Retrieved September 30, 2010, from http://www.chemistry.ccsu.edu/glagovich/teaching/316/qualanal/tests/hinsberg.html

Hunt, D. I. (n.d.). Chapter 22: Amines. Retrieved September 25, 2010, from http://www.chem.ucalgary.ca/courses/350/Carey/Ch22/ch22-1.html#Properties

Morrison, R. T., & Boyd, R. N. (1992). Organic Chemistry 6th. Ed. Pearson Education Inc.

Most, J. C. (1988). Experimental Organic Chemistry. John Wiley & Sons.