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CLASSIFICATION TESTS FOR ORGANIC HALIDES FORMAL REPORT

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Formal Report in Organic Chemistry. University of Santo Tomas
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  CLASSIFICATION TESTS FOR ORGANIC HALIDES Venus Tibalao, Cheene Meryll Urmatam, Abby Valdesancho, Gian Paula Villamayor, Ramon Villanueva III and Thea Ferina Vital  Group 9 2C Pharmacy Organic Chemistry Laboratory ABSTRACT Alkyl halides or commonly known as haloalkanes are organic compounds that involves the replacement of a halogen atom to an alkane. This study aimed to identify the rate of reaction of a haloalkene, chiefly n -butyl chloride, sec  -butyl chloride, tert  -butyl chloride and chlorobenzene in an S N 1 and S N 2 mechanisms. Initially, the presence of a halogen in an alkane was indicated by Beilstein Test. It was found out that the presence of a halogen gives of a green-flame to the test. Thenceforth, reactivity of the said compounds in an S N 1 reaction was tested by reacting them with Alcoholic AgNO 3 . Only the secondary and tertiary butyl chloride produced a reaction (in the form of a white precipitate) in this mechanism, but the former haloalkane acquired a faster reaction time because it produces the most stable carbocation which is a prerequisite for a certain haloalkane to react in an S N 1 reaction. Normal butyl chloride did not react because of its high instability when it becomes a carbocation. Lastly in S N 2 mechanism, the haloalkanes were made to react with NaI in Acetone. All haloalkanes, except for chlorobenzene, produced a white precipitate in the reaction mechanism. However, n -butyl chloride had the fastest response time because of its low steric hindrance. The said property of normal butyl chloride explains its susceptibility to S N 2 reaction. The unresponsiveness of chlorobenzene is due to its high stability acted upon by the resonating effect of its conjugated double bonds.  INTRODUCTION Haloalkanes are organic compounds having a halogen atom covalently bonded to an sp 3 hybridized carbon. Since halogens are more electronegative than carbons, the carbon-halogen bond in a haloalkane is polarized. Chlorofluorocarbon is a well-known example of a haloalkane. They are used as refrigerants, propellants for aerosols, for generating foamed plastics and solvents for dry cleaning. However, CFCs are responsible for the destruction of ozone layer that is why the use of these compounds is now in limitation. The objective of this experiment is to identify the different properties and reaction rate of haloalkanes through the use of Beilstein Test, Reaction with Alcoholic AgNO 3 and Reaction with NaI in Acetone.   EXPERIMENTAL A. Compounds tested (or Samples used) The compounds tested were n -butyl chloride, sec  -butyl chloride, tert  -butyl chloride and chlorobenzene. The information of the said compounds is stated below: n -butyl chloride The figure below is the structural formula of a normal butyl chloride (n-butyl chloride). It is a clear, colorless liquid. It is used as a solvent, as a medicine to control worms, and to make other chemicals. Exposure to the said substance can infuriate the eyes, nose, throat and skin. Highlevels of Butyl Chloride causes dizziness and syncope. It is a flammable liquid and a fire hazard.   Figure 1: Chemical Structure of n-butyl chloride sec  -butyl chloride Figure 2 presents a secondary butyl chloride or 2-Chlorobutane. It is a clear, colorless liquid with a sharp odor. Its vapors may form explosive mixtures with air.   Figure 2: Chemical Structure of sec-butyl chloride tert  -butyl chloride Figure 3 shows a tertiary butyl chloride. It is a clear, colorless liquid which is slightly soluble in water. Inhalation of high concentrations may cause central nervous system effects  characterized by headache, dizziness, unconsciousness and coma. Figure 3: Chemical Structure of tert-butyl chloride Chlorobenzene The figure beneath is a chlorobenzene. uses of chlorobenzene are as a solvent for pesticide formulations, diisocyanate manufacture, and degreasing automobile parts and for the production of nitrochlorobenzene.In the past, chlorobenzene was used as an intermediate in phenol and DDT production. Figure 4: Chemical Structure of chlorobenzene B. Procedure The following tests used in this study are indicated as follows: 1.   Beilstein Test: Copper Halide Test a.   A small loop was made with one end of the copper wire. The loop was directly heated in the oxidizing zone of a non-luminous flame. The heating was continued until the green color imparted to the flame disappeared. b.   The loop was cooled slightly and dip it into the solid or liquid sample. The loop was heated with the sample in a non-luminous flame: first in the inner zone, then in the outer zone near the edge of the flame. 2.   S N 1 Reactivity: Reaction with Alcoholic AgNO 3  a.   5 drops of the sample was added to 20 drops of 2% ethanolic AgNO 3 . The sample was shaked and the time for a silver halide precipitate to form was recorded in seconds or minutes. 3.   S N 2 Reactivity: Reaction with NaI in Acetone a.   Dry test tubes was used for this experiment. 5 drops of the sample was added to 2 drops of 15% NaI in anhydrous acetone. The contents were mixed the time was noted (in seconds or minutes) required precipitate to form. The color of the precipitate was described RESULTS AND DISCUSSION The sample of haloalkanes were subjected in the following reactions, namely, Beilstein test, S N 1 Reactivity (Reaction with Alcoholic AgNO 3 ), and S N 2 Reactivity (Reaction with NaI in Acetone). Primarily, the data acquired from Beilstein Test was the haloalkane’s color when exposed to flame. Table 1. Data obtained from Beilstein Test Compound used Color of the flame n -butyl chloride Green sec  -butyl chloride Green tert  -butyl chloride Green chlorobenzene Green Green flame, shown by Table 1, indicated the presence of a haloalkane, particularly Chloride. The equation for this test is presented below. When you heat the copper wire in a flame, it is oxidized on the surface to copper (II) oxide. 2Cu(s)+O 2 (g) ⟶ 2CuO(s) A positive Beilstein test is based upon the reaction of the Organic halide with the Copper oxide: CuO + RX --> CuX 2  + CO 2  + H 2 O The volatile copper halide (CuX 2 ) compound gives the flame test a blue-green colered flame. Table 2.  Data obtained from S N 1 Reactivity Compound used Reaction and time achieved from reaction n -butyl chloride No precipitate sec  -butyl chloride White precipitate (3 min and 10 sec) tert  -butyl chloride White precipitate (1 sec) chlorobenzene No precipitate Secondly, S N 1 Reactivity was acquired from reacting 2% ethanolic AgNO 3  with the given haloalkanes. This reaction will identify if the  samples given produced a precipitate. The time of response or rate of reaction to generate a precipitate indicates the nature of haloalkanes toward S N 1 reaction.   It appears that n -butyl chloride and chlorobenzene did not react with the said reaction. A primary haloalkane does not have an inherent effect in S N 1 reaction because it does not provide a stable carbocation. S N 1 Reactivity depends on the stability of the carbocation. The more stable a carbocation, the more susceptible a haloalkane to react   in an S N 1 reaction . Chlorobenzene did not react in the because of the stabilizing or resonating effect of conjugated double bonds in benzene. Figure 4: Reaction mechanism of S N 1 Reaction The figure above shows the reaction mechanism of S N 1 Reaction. This shows a two-step reaction of the said mechanism. S N 1 Reactions greatly depend on the nature of the leaving group, particularly the halogens. Reactivity depends on the stability of the carbocation. The more stable a carbocation, the more susceptible a haloalkane to react in an S N 1 reaction. Table 3.  Data obtained from S N 2 Reactivity Compound used Reaction and time achieved from reaction n -butyl chloride White precipitate (1 sec) sec  -butyl chloride White precipitate (2 sec) tert  -butyl chloride White precipitate (3 sec) chlorobenzene No precipitate In this reaction, only chlorobenzene failed to react in S N 2 mechanism because of its high stability due to Benzene’s resonating effect. S N 2 reaction prefers a primary haloalkane because nucleophilic attack occurs simultaneously with the leaving group. The more substituents attached to the alpha carbon, the less tendency for a nucleophile to attack the said carbon. This accounts for the reason why a tert-butyl chloride reacts slowly in an S N 2 reaction. The figure below explains the 1-step mechanism of S N 2 reaction. The said reaction depends on the nucleophile and the leaving group. Figure 5: Reaction mechanism of S N 2 Reaction The figure above explains the 1-step mechanism of S N 2 reaction. The said reaction depends on the nucleophile and the leaving group. REFERENCES [1] Bayquen,A.,Cruz,C., De Guia,R. Lampa, F., Pena, G., Sarile, A., Torres,P. Laboratory Manual in Organic Chemistry, pp.27-28 [2] Brown, H., and Poon, T. P. Introduction to Organic Chemistry  , pp. 250 [3] www.drugfuture.com/chemdata/sec-butyl-chloride.html [4]www.chemicalbook.com/ProductMSDSDetailCB3372184_EN.htm [5]chemwiki.ucdavis.edu/Organic_Chemistry/Alkyl_Halides/Properties_of_Alkyl_Halides/Haloalkanes
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