Alcohols react with hydrogen halides (HCl is used in this experiment) to yield the resultant alkyl halides and water. The insolubility of the alkyl halide in water allows the separation of it from the aqueous layer using a separatory funnel. The alkyl halide, then, were purified by a simple distillation apparatus using boiling point differences between the pure tert-butyl chloride and not. In this experiment, tert-butyl chloride is synthesized from tert-butyl alcohol. Introduction Alkyl Halides (also known as halogenoalkanes or haloalkanes) are a group of chemical compounds derived from alkanes containing one or more halogens.
They are a subset of the general class of halocarbons, although the distinction is not often made. Alkyl Halides are widely used commercially and, consequently, are known under many chemical and commercial names. A number of methods were developed for its systematic synthesis. The most common preparation method is by reacting alcohol with hydrogen halides in extremely acidic environments. In this production method, tertiary alcohols were recommended to be used because of the stability and relative strength of the tertiary carbocation.
Halogens will substitute with the hydrogen atoms to form alkyl halides through SN1 reactions. Experimental Detail Before all else, the materials and the simple distillation set-up were prepared. 10 mL tert-butyl alcohol and 20 mL cold concentrated HCl was placed in a dry 30 mL separatory funnel while gently swirled. It is important to use cold concentrated HCl because keeping the temperature of the acid low will increase the fraction of the SN1 product so to increase the yield. Keeping it cold will help prevent loss of the volatile product after it is formed.
The mixture was relieved by the internal pressure by slowly opening the stopcock from time to time. The mixture remained undisturbed for about 20 minutes then its layers were separated by removing the aqueous layer (To determine which the aqueous layer is, add 1-2 drops of water in each layer. The layer in which the water dissolves is the aqueous layer, which will be discarded into the waste acid bottle). The organic layer was then transferred into a dry flask which contained a small amount of solid NaHCO3.
Solid NaHCO3 is the primary standard for acid-base titrations because it is firm and air-stable, making it easy to weight accurately. It is also used to speed up the decomposition of water in electrolysis. Again, it was swirled gently and decanted into another dry flask. The filtrate was then dried with anhydrous CaCl2 and decanted into a dry 25 mL round bottom flask. The crude alkyl halide product must be dried carefully with anhydrous CaCl2 before distillation to prevent hydrolysis of the Alkyl Halide during the distillation of the product.
A few boiling chips were added to prevent it from suddenly overheating and the crude tert-butyl chloride was distilled. Without boiling chips, a liquid which is heated in a horizontal container might become superheated and "bump' all of a sudden, and occasionally discharges vapor. This sudden discharge of gas might result in the solution as well as the reagents to be spilled out of the container all of a sudden. A simple distillation set-up was prepared as shown in Figure 1. In simple distillation, the liquid to be boiled is placed in a vessel which is usually made of metal or glass.
The vessel is known as a retort. The top of the container is curved downward. At the bottom of the condenser’s cooler, a steady flow was being observed to prevent an increase in pressure inside the condenser. The sample was heated slowly and the temperature rose rapidly then remained constant at the boiling point of the sample. The temperature should be recorded. When the sample started to boil, the heat was removed and left to cool down before it was disassembled. The pure tert-butyl chloride was then collected and placed in a 10 mL graduated cylinder cooled in an ice bath.
The fraction that boiled at 49-52 ? C was the one collected and submitted to the instructor in a labeled vial. Figure 1. Simple Distillation set-up Results and Discussion The synthesis of alkyl halides was done by adding hydrogen halide, HX (in this experiment, HCl was used). Using tertiary alcohol is most recommended from the synthesis of alkyl halides because it is the most stable and it will react quickly to the reagent. HBr and HI can more readily undergo homolytic cleavage (one electron to each atom) than HCl, since the halogens are not so electronegative. Thus, with a little push, e. g. y a peroxy radical that steals an H atom, these two acids can form bromine and iodine atoms, which can undergo free radical chain reactions.
This reaction is the reason for the "antimarkovikov" addition of HBr to alkenes. In the upper atmosphere, chlorine atoms too can survive, and both chlorine and bromine atoms are responsible for free radical chain reactions with convert ozone (O3) back to dioxygen, thus destroying the ozone layer which protects the earth from the near ultraviolet light from the sun. Alkyl halides always undergo SN1 and they reacted using nucleophilic substitution (attached to a sp3-hybridized ion).
Boiling chips better known as boiling stones or anti-bumping granules basically are minute, unevenly shaped stones added to liquids so that they can boil easily. They offer nucleation sites so that the fluids can boil quickly without turning superheated. Without boiling chips, a liquid which is heated in a horizontal container might become superheated and "bump” all of a sudden, and occasionally discharges vapor. This sudden discharge of gas might result in the solution as well as the reagents to be spilled out of the container all of a sudden.
Boiling chips generally are made from absorbent matter like alumina, calcium carbonate or carbon, and normally come with non-reactive glaze of Teflon, which makes sure that the boiling chips will offer effective nucleation spots. In this experiment, simple distillation was used. This is where all the hot vapors produced are immediately channeled in a condenser that cools and condenses the vapors. The distillate will not be pure. Its composition will be identical to the composition of the vapors at the given temperature and pressure, and can be computed from Raoult’s law.
Simple distillation is usually used only to separate liquids whose boiling points differ greatly or to separate liquids from involatile solids or oils. 2-Methylpropene boils at over 50 degrees lower than tertiary butyl chloride, so that suggests the distillation, collecting product around the boiling point of the chloride, should do the trick. Conclusion Toward the conclusion of the experiment, the objectives of the undertaking were secured. From tert-butyl alcohol, tert-butyl chloride was synthesized using a hydrogen halide and simple distillation. The experiment was accomplished.