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 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 RNH 2, 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 (RNH 2), 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 Aniline
SOLUBILITY IN WATER Not soluble
LITMUS TEST Acidic
N,N-Dimethylaniline
Not soluble
Acidic
Diethylamine
Soluble
Basic
ADDITION OF CONC. HCl Presence of gas which made the compound miscible with the reagent Smoke was emitted but the compound remained immiscible The smoke emitted remained contained in the tube on top of the compound
Table 2. Chemical Property of Amines and their Classification HINSBERG TEST AFTER ADDITION OF BENZENE SULFONYL CHLORIDE
Aniline Milky, heterogenous appearance of liquid
AFTER ADDITON OF CONC. HCl AFTER WARMING WITH 10% NaOH AMINE CLASSIFICATION Discussion of Results
Presence of crystals Soluble Primary
N,N-Dimethylaniline Presence of green substance and the liquid appears in 2 phases Formation of gel-like substance Immiscible with blue color of solution Tertiary
Diethylamine Milky, homogenous appearance of liquid
Formation of milky gellike substance immiscible Secondary
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,NDimethyllaniline 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. Q uestions 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-
C6H5NH2 + C6H5SO2Cl
+
NaOH
[C6H5SO2NHC6H5]
-
+
H
C6H5SO2NC6H5 Na
C6H5SO2NHC6H5
Diethylamine: -
OH
CH3CH2NHCH2CH3 + C6H5SO2Cl
NaOH or H
[C6H5SO2NH(CH3CH2)2]
+
No reaction
N,N-Dimethylaniline: OH-
C6H5N(CH3)2 + C6 H5SO2Cl
c.
NaOH
[C6H5SO2(CH3)2 NC6H5]
+
C6H5SO2(CH3)2 NC6H5Na
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
C hemistry 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 T est . Retrieved September 30, 2010, from http://www.chemistry.ccsu.edu/glagovich/teaching/316/qualanal/tests/hinsberg.html Hunt, D. I. (n.d.). C ha pter 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 C hemistry . John Wiley & Sons.
