Exp 9 Alkenes from Alcohols Analysis of a Mixture by Gas Chromatography PDF

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Alkenes from alcohols: Analysis of a mixture by Gas Chromatography Dennis Rossi and Roger Mendez CHM 2210L TA: Suzeeta Bhandari March 25 , 2019

Intro This experiment goes through a process called an elimination reaction. There are two types of elimination reactions: E1 and E2. This process is where an HX substituent is removed to form a double bond between two carbons. When the base attacks to remove the HX substituent, that spot is usually where the carbon cation is formed (Solomon, 2016). However, there can be a carbon cation rearrangement where there is either hydride shift, methyl shift, or a ring expansion. The double bond usually forms between the two carbon that the bond has the must substituent because this makes the molecule more stable. The E1 reaction is a unimolecular reaction where there is a removal of an HX substituent that forms a double bond. This process is very like SN1 where there is a formation of an intermediate carbon cation (Libretexts, 2015). SN1 and E1 always compete with each other. There will be times where the products are formed simultaneously through one reaction because the processes are very similar and require the same factors to react. The only way to be sure that a certain chemical will form is by changing the thermodynamics (Libretext, 2015). E1 favors carbons just like SN1 where the alkyl halide is tertiary > secondary > primary > methyl. This reaction is the reaction that occurred throughout this experiment forming 2-methyl-2-butene and 2-methyl-1-butene from 2-methyl-2-butanol (Weldegirma, 2019). The E2 reactions are much more specific than E1 because it requires a strong base to occur and it mainly occurs in secondary and tertiary alkyl halides. However, if a bulky base is being used then it could also occur through a primary alkyl halide (Libretext 2015). E2 reactions occur in one process like SN2, however, it does not compete with SN2. This is because E2 need

strong bases that mainly occur in secondary and tertiary alkyl halides. On the other hand, an SN2 requires weak bases and strong nucleophiles to occur. In general, the factors affecting the rate of E1 and E2 reactions are the nature of the alkyl halide and the nature of the reagents. For example, in order for an E 1 to occur the alkyl halide must be tertiary and secondary. If the alkyl halide was secondary or tertiary than it must have a weak base to occur if it has a strong base than an E2 reaction will occur. E2 reaction favors tertiary and secondary alkyl halides, however, an E2 reaction may occur in a primary alkyl halide if the strong base is bulky therefore creating steric hindrance (Solomon, 2016). Reaction

Side reaction

Experimental Section

1.5 mL D.I. H2O was put into a 10 mL conical vial . Then 1 mL H2SO4 was put in drop wise and mixed

The distillation was ran at 30-45 oC. And was stopped when the rate of drips exponentially decreased

The solution was cooled in an ice bath. Then 2 mL of 2-methyl-2-butanol was added with boiling stones and shacked well

The collecting vial was preweighed with CaCl2 pellets.

A simple distillation was set up

The collection was removed to weigh and calculate the percent yield

Gas Chromatography:

It was injected into the gas chromatography and all the conditions were recorded

Using a clean syringe, 0.1 mL of the sample was extracted

The gas chromatography was ran and the results were received

The percent was calculated of each compound

Table of Chemicals Molecular

Molecular

Melting

Boiling

Density

formula

weight

Point

point

(g/cm3)

(g/mol)

(oC)

(oC)

Structure

Sulfuric acid

H2SO4

98.027

10

330

1.84

2-methyl-2-

C5H12O

88.15

-12

101-

0.815

butanol

103

2-methyl-1-butene

C5H10

70.135

-137.5

31.2

0.65

Calcium chloride

CaCl2

110.98

782

1600

1.086

2-methyl-2-butene

C5H10

70.13

-133.7

38.5

0.65

Sulfuric acid

Calcium chloride



May be corrosive to metals



Harmful if swallowed



Causes sever skin burn



Causes serious eye damage



Causes severe eye damage



May cause respiratory irritation



Keep container tightly closed in well-



Cause damage to organs through

ventilated area

prolonged or repeated exposure 

2-methyl-2-butanol

Keep container tightly closed in well-



Highly flammable



Causes serious eye damage



May cause drowsiness or dizziness



Harmful if swallowed



Causes skin irritation



Highly flammable



Harmful if inhaled



Causes skin/eye irritation



Keep container tightly closed in well-



May cause drowsiness or dizziness

ventilated area



Harmful if inhaled



Suspected of causing cancer

ventilated area 2-methyl-1-butene

2-methyl-2-butene 

Harmful if swallowed



Suspected of causing genetic defects



Highly flammable



Keep container tightly closed in well-



Causes skin/eye irritation



May cause drowsiness or dizziness



Harmful if inhaled



Suspected of causing cancer



Suspected of causing genetic defects



Keep container tightly closed in well-

ventilated area

ventilated area

Results Mass od 2-methyl-2-

Alkenes (2-methyl-1-

butanol (g) 1.6

Mass of alkenes (g)

Percent yield

0.159

(%) 9.9375%

butene and 2-methyl-2butene)

Percent yield ( % )=

experimental x 100 theoretical

Percent yield ( % )=

0.159 x 100 1.6

0.159 x 100 =9.9375 1.6 Percent yield=9.9375 %

Gas Chromatography

The second peak is 2methyl-2-butene and the amount is 89.1%

The first peak is 2methyl-1-butene and the amount is 10.9%

Discussion The experiment performed gave results that were less than ideal. The percent recovery that was calculated was way less than 50 %, it was 9.9375%. when ideally the percent yield should have been above 50% because 2-methyl-2-butanol produced a mixture of two chemicals so the percent recovery would have been one plus the other making it higher. There are several reasons why the percent yield might have been so low. The first reason could be due to human error, where the simple distillation was stopped really early and the complete amount could not have been recovered. Another reason for some loss may be that some of the solution was lost as vapor, escaping through the gaps of the simple distillation setup. A third reason may be due to mechanical error where the sand bath wasn’t heating fast enough to allow the reaction to

complete. Also while performing the experiment there were problems with the outlets, for power, and the water circulation for simple distillation. The percent recovery was so low that gas chromatography was not able to be performed. The data on the gas chromatography was gathered from a different group's results. In the gas chromatography, there are two main peaks the shorter one is the most volatile and the largest one is least volatile. Volatile means the substance that is easily evaporated. Therefore the first peak is 2-methyl-1-butene is the most volatile because its boiling point (31.2oC) is the lowest and there is 10.9% of this alkene in the solution. On the other hand, 2-methyl-2-butene is the least volatile because the boiling point (38.5oC) is the highest and it will evaporate second. The amount of 2methyl-2-butene in this solution is 89.1%. Some explanations why 2-methyl-1-butene is more volatile is because according to Zaitsev’s rule the least substituted product is the minor product and the most substituted product is the major product, hence why 2-methyl-2-butene is the major product. Conclusion The theoretical background and the results that were gathered, do correlate to an extent with each other. The background suggested that a mixture of 2-methyl-2-benzene and 2-methyl-1benzene will be formed from 2-methyl-2-butanol. However, the yield of this mixture was very low that suggested that something went tremendously wrong during the experiment that prevented higher yield of this mixture. The data reveals that not enough mixture was collected to perform a gas chromatography, therefore, another group’s data was used. The technique that was performed could be useful. Because elimination mechanisms are reversible, alkenes can be used to make alcohols that are used in many aspects, medicine, beer or wine, synthetic or rubber (Libretext, 2017). Also, there are multiple uses of alkenes, from plastic to make polymers and

from polymers, different polymers are able to be synthesized such as PV, telfon, or plexiglas (Chemgaroo, 2019). References All Uses of Alkanes, Alkenes, and Alkynes in Industry and Many Fields. https://azchemistry.com/uses-of-alkanes-alkenes-and-alkynes-in-industry (accessed Mar 26, 2019). Libretexts. 14.3: Elimination by the E1 and E2 mechanisms. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Book:_Organic_Chemistry_with_a_ Biological_Emphasis_(Soderberg)/14:_Reactions_with_stabilized_carbanion_intermediates,_par t_II/14.3:_Elimination_by_the_E1_and_E2_mechanisms (accessed Mar 26, 2019). Libretexts. Uses of Alcohols. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_C hemistry)/Alcohols/Properties_of_Alcohols/Uses_of_Alcohols (accessed Mar 26, 2019). Solomons, T. W. G.; Fryhle, C. B.; Snyder, S. A. Organic chemistry; John Wiley et Sons, Inc.: Hoboken, NJ, 2016. Weldegirma, Solomon. “Experiment 9: Alkenes from Alcohols: Analysis of a mixture by Gas Chromatography.” Experimental Organic Chemistry. 8th Edition, Tampa, Pro-Copy Inc.2018. 50-49.’ zum Directory-modus.

http://www.chemgapedia.de/vsengine/vlu/vsc/en/ch/12/oc/vlu_organik/alkene/indust_bedeut_alk ene.vlu/Page/vsc/en/ch/12/oc/alkene/polymere_werkstoffe/polymere_werkstoffe.vscml.html (accessed Mar 26, 2019)....