2nd order bimolecular nucleophilic substitution reactions
they are unique in that they complete bond-breaking and
bond-forming simultaneously. The alcoholic reactants
used in this experiment are very common in substitution
reactions when used with hydrogen halides. The
mechanism that occurs between an alcoholic compound
and hydrogen halide varies depending on the structure of
the alcoholic reactant.
The purpose of this experiment is to determine the
structure of the product(s) and compare them to the
structure of the original starting material to determine if
the reaction was an SN1 or SN2 mechanism.
Analysis of Substitution Reactions with Alcoholic
Compounds
(Name)
IUPUI Organic Chemistry Lab, LE 207. 402 N. Blackford
St., Indianapolis, IN 46202
jordjohn@iupui.edu
(1)
Scheme 1. Substitution
bromopropane.
of
1-propanol
to
form
1-
(2)
(1)
(3)
Reaction 1, the primary alcohol resulted in the above
product with an 37% yield using reflux with sodium
bromide and sulfuric acid. Following reflux distillation
was carried out to separate the unwanted liquid products
from the desired product. Using 1H NMR it was
determined there were no other products that resulted.
Subjecting the product to gas chromatography resulted
in a very major peak consisting of 88% and a minor
peak of 12% . IR spectra was gathered but resulted in
peaks indicating structures that should not have
appeared.
The results of several substitution reactions with hydrogen
halides will be reported. The method of substitution
appears dependent, in large part, on the properties/identity
of the alcoholic starting material. Synthetic methodology
and an explanation of resulting substitutions are discussed
herein.
The reactions included in this journal were completed as
group to educate the idea of chemistry research. In a true
research laboratory a given set of directions does not
come with each experiment but only trial and error to
understand a reaction. Basic organic chemistry
laboratory skills such as distillation, reflux, and
spectroscopy were applied in this experiment. A sample
journal article containing similar alcoholic substitution
reactions we used as a guide for preparing the reactions
as well writing a journal article that might be found in
the Journal of Organic Chemistry. Excluding the use of
the sample journal article, all reactions were completed
without the aid of a given set of directions from a
laboratory textbook.
This journal investigates substitution reactions
containing alcoholic compounds with hydrogen halides.
Substitution reactions are very helpful in the
development of synthetic materials. Substitution occurs
with the replacement of one  (sigma) bound atom with
another  bound atom. There are two types of
substitution reactions SN1 and SN2. SN1 are 1st order
unimolecular nucleophilic reactions which proceed
through a rate-determining step forming a carbocation
before substitution, forming the final product. SN2 are
Scheme 2. Substitution of 2,4-dimethyl-3-pentanol to
form 2-chloro-2,4 dimethylpentane or 3-chloro-2,4dimethylpentane.
(2)
Reaction 2, a secondary alcohol mixed with
hydrochloric acid and zinc chloride, resulted in 48%
yield by way of reflux. The reaction produced two
products because of a hydride shift in order to form a
more stable tertiary carbocation, therefore forming a
tertiary major product. The minor product is the result of
direct substation to the unaltered intermediate. Product
was collected as any oily liquid. Analysis of the product
with gas chromatography resulted in two peaks
indicating the possibility of two products. Analysis of
the products with 1H NMR did not produce any peaks
indicating protons that were adjacent to the halogen. The
reason this could have occurred was the resulting
products had similar polarity/structure. IR spectroscopy
1
was difficult resulting major peaks indicating sp3 carbon
atoms.
reflux for 20 minutes. Following reflux the reaction
mixture was washed with two 10 mL portions of water
then separated by density organic product was top layer.
Organic product was dried using sodium sulfate.
Product 2 was collected and weighed (0.86 g, 0.00639
mol, 48%). 1H NMR, IR, and GC were collected to
analyze the product. 1H NMR (CDCl3, 200 MHz) 0.91.10 (sext, 7H) 1.65 (s, 6H) 1.7 (t, 2H). IR (cm-1) 2961,
2871, 1467, 1385, 1155, 1101. GC (TCD) 4m (51.4%)
5m (48.6%)
Scheme 3. Substitution of 2-pentanol to form 2bromopentane and 3-bromopentane.
(3)
Reaction 3 produced the above products from the
secondary alcohol in a 9% yield. The reactant was
combined with sodium bromide and sulfuric acid then
refluxed for 20 minutes until two layers resulted.
Following reflux, distillation was performed until a dark
brown white paste resulted. Analysis of the product with
gas chromatography presented two peaks after
comparison to the starting material gas chromatography
it was determined only one peak was desired product.
2-bromopentane and 3-bromopentane (3) Preperation
required the alcoholic starting material 1.75 g (.0015
mol) and sodium bromide (3.38 g.033 mol) to be added
to 8 ml 9M H2SO4. Heat under standard reflux under
conditions for 20 minutes. While under reflux, the
reaction developed 2 layers. Following reflux the
reaction material was distilled until a dark brown wet
paste remained. Care was taken not to let the distilling
pot heat to dry. Extraction of the distillate with 1 x 15
mL of water and 2 x 10 mL of 5% NaCHO3 afforded the
oil 3 (1.1g, .0071 mol, 9%). 2-bromopentane/3bromopentane 1H NMR (CDCl3, 200 MHz) 2.160
(s,7H), 1.65 (s,3H) IR (cm-1) 3456, 2097, 1644, 692,
414. GC (TCD) 2..3 m (82.76%) 4.5 m (17.25%)
Experimental Section
All reactions were carried out under normal
atmospheric conditions. Chemicals were used directly
from the manufacturer’s bottle unless otherwise
mentioned. All work-ups are specifically detailed in the
procedures below. 1H NMR spectra were gathered
using a Varian Gemini 200 MHz spectrometer. IR
spectra were gathered using a Thermo-Nicolet 380 FTIR. Gas chromatographs were obtained using a GOWMAC 69-400-TCD GC.
Acknowledgement. This work was made possible by
the Department of Chemistry and Chemical Biology at
Indiana University Purdue University at Indianapolis.
References.
1. Denton, R.E.; Audu, C. “Investigating Substitution
Reactions of Various Alcoholic Compounds.” Journal of
Organic Chemistry 2010, 77, 3452-3453.
1-bromopropane (1). Preparation of 1 was achieved by
adding 1-propanol (1.12 g, 0.0186 mol), sodium
bromide (7.00 g, 0.0680 mol), and 12 mL 9M sulfuric
acid to a 100 mL round-bottom flask. Boiling chips
were added to help with the refluxing. This mixture was
refluxed for 20 minutes. During reflux, there were no
distinct layers observed. After reflux, the mixture was
distilled until no more liquid dripped from the West
condenser. The distillate was then separated using one
15 mL wash with water followed by two washes of 5%
NaHCO3 made by mixing 1 g of NaHCO3 with 20 mL of
water. Solution was then eliminated of water by using
anhydrous sodium sulfate.
NMR (CDCl3, 200MHz) δ 4.801-4.805 (d, 3H),
4.787-4.792 (t , 2H), 1.644-1.647 (d, 2H). IR (cm-1)
3480, 2361, 2077, 1636, 1360, 598. GC (TCD) 3.18 m
(88.0%) 4.76 m (12.0%)
1H
2-chloro-2,4-dimethylpentane and 3-chloro-2,4dimethylpentane. (2) Mixture made with alcoholic
starting material (1.78 g, 0.0153 mol) and 5mL Lucas
reagent added in a round-bottom flask and heated under
2