EXPERIMENT 8 SUBLIMATION AND MELTING POINT DETERMINATION SUNGLAO, A., A. , SUPAN, E., E., TAN, C., TAYAG, P, TUASON, A. GROUP 9, G, FACULTY OF PHARMACY, UST
Abstract Organic halides are the compounds that contain one or more halogen atoms in addition to carbon and hydrogen. These organic compounds are usually synthetic and nonflammable. The objectives of the said experiment is to differentiate primary, secondary and tertiary organic halides based on their S N reactivity and differentiate S N1 and S N2 mechanisms with organic halides. In the experiment conducted by the group, the organic compounds n-butyl chloride, sec-butyl chloride, tert-butyl chloride and chlorobenzene, were subjected to Reaction with alcoholic AgNO 3 and reaction with NaI in Acetone. Although Beilstein Test is one of the tests to be performed, however was not conducted due to having to yield with positive results since all of the compounds contain halides, specifically chloride. Compounds n-butyl chloride, sec-butyl chloride, tert-butyl chloride and chlorobenzene when reacted with alcoholic AgNO 3 resulted to a turbid solution and white precipitate. For the S n2 Reactivity: Reaction with the NaI in acetone yielded with a white precipitate in the organic compounds.
INTRODUCTION Organic halides are compounds with a halogen atom bonded to a saturated sp3hybridized carbon atom. Carbon halides are known because of its large variety. Halogens can be bonded with an alkynyl group (C=C-X), an aromatic ring (Ar-X) or an alkyl group. These halogens can be of elements chlorine, bromine, fluorine and iodine. The organic compounds are considered to be non-flammable and most of organic compounds are synthetic. Moreover, if alpha carbon is tetragonal or sp3 hybridized in the compound, the organic halides may be classified as primary, secondary or tertiary, depending on the substitution of the alpha hydrogen atom by an R group. The structures of the following compounds are as follows:
N -butyl chloride
sec-butyl chloride
Tert-butyl chloride
chlorobenzene
Reactivity of these types of organic halide depends on the substitution of reaction with a nucleophile, wherein a single molecule of one group or atom replaces another. There are basically two types of reaction substitution in organic halogens, Sn1 reactivity and S n2 reactivity. S n1 reactivity or unimolecular reaction happens when the reaction is dependent to the organic halide and the specie is involved in the rate determining step. It has a rate equation of Rate= k[RX], where k is the constant on what the species is actually involved. The equation clearly conveys that even if one doubles the concentration of the nucleophile, there will still be no effect in the rate of reaction. However if the
concentration of the alkyl halide will be cut into half, then the mechanism will slowed down by half.S n2 reactivity or bimolecular reaction on the other hand happens when the rate of reaction is dependent both on the organic halide and the nucleophile, giving a rate equation of Rate = k[Nuc][RX], where k is a constant based on what species are actually involved. Both of the species are part of the rate determining step. The organic compounds are subjected to three test for it to be classified accordingly. One test is called, Beilstein Test. Beilstein test is developed by a Russian scientist named Friedrich Konrad Beilstein, and this is a simple chemical test used in chemistry as a qualitative test for halides. In this test, you will be using copper wire looped at the end to get an amount of sample compound and heat the hoop directly at the oxidizing zone of a nonluminous, continuously do the procedure until one would produce excited, greencolored copper atoms or ions that cause
the normally colorless (or very slightly blue) flame to flare brilliant green (or sometimes blue-green). The green flame in this test indicates formation of a copper halide. Another test for organic compounds is the Sn1 reactivity, where the compounds are going to be reacted with alcoholic AgNO 3 resulting to a white precipitate among the compounds, n-butyl, sec-butyl and tertbutyl. Chlorobenzene was not able to produce a precipitate due to its resonance giving stability to the compound, which it wouldn’t react unless used with a catalyzing agent. SN2 Reactivity: Reaction with NaI in Acetone, this complements the alcoholic AgNO3, and when these two sets are used together, is possible to determine accurately the gross structure of the alkyl group. In this reaction, iodide ion serves as the nucleophile; the order of reactivity is primary > secondary > tertiary. This test will result to white precipitate due to the presence of halides, except for chlorobenzene which again will not react to the said test.
MATERIALS AND METHOD A. Samples used n-butyl chloride sec-butyl chloride tert-butyl chloride chlorobenzene
B. Procedures 1. SN1 reactivity Add 5 drops of sample to 20 drops of 2%ethanolic AgNO 3 . Shake and record the time in seconds or minutes for a silver halide precipitate to form. Then describe the color of the precipitate. 2. Sn2 reactivity Use dry test tubes for this experiment. Add 5 drops of the sample to 2 drops of 15% NaI in anhydrous acetone. Mix the contents and note (in seconds or minutes) required for a precipitate to form. Then describe the color of the precipitate.
RESULTS AND DISCUSSIONS 1. Data obtained from S N1 Reactivity: Reaction with Alcoholic AgNO 3
Table 1
Compounds used
Reaction/Results
Time
n-butyl chloride
White flaky precipitate
4 min. and 12 sec
sec-butyl chloride
Slightly turbid
3 min and 55 sec
Tert-butyl chloride
White precipitate
2 min and 43 sec
chlorobenzene
Cloudy when shaken
5 min 18 sec
In the S N1 Reaction, the first compound to produce a precipitate was tert-butyl chloride, which appeared after 2 mins and 43 sec, followed by s ec-butyl chloride which appeared after 3 min and 55 sec, n-butyl chloride which came third at 4 min and 12 sec lastly chlorobenzene which was the last to precipitate that lasted 5 min 18 sec. The kinetics of the reaction is dependent to the alkyl halide. The more stable the carbocation intermediate, the faster the rate of reaction in Sn1. 2. Data obtained from the S N2 Reactivity: Reaction in NaI to Acetone Table 2 COMPOUNDS
REACTIONS/RESULTS
n-butyl chloride
White ppt.
sec-butyl chloride
White ppt.
tert-butyl chloride
White ppt.
chlorobenzene
White ppt.
In the S N2 experiment, the first to show precipitate was the n-butyl chloride, next to it is the secbutyl chloride followed by tert-butyl chloride and last is the chlorobenzene. The reaction of this experiment was dependent on the alkyl halide and the nucleophile. Due to steric effect the substrate effect in S N1 reaction is opposite in S N2 reactions. It favors primary and secondary substrates. Strong nucleophile was needed for the reaction to occur because it parallels basicity.
CONCLUSION (Al jan palagay nalang yung conclusion mo dito na nasa inference mo, mas matino ata yung sayo e. Thanks Al Jan! Love you! )
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