Teo Davidian
ID # 57891107
Chemistry 107L
Monday 3-9:50
Lab Partner: Irmak Sengur
POL: Synthesis and Catalysis of Organic and Inorganic Compounds
Abstract:
For this week’s lab, the glovebox was introduced because of the use of air sensitive compounds. The coordination polymerization of ethylene was synthesized in Part I by a Ziegler-Natta catalyst. The polymerization of inorganic monomers is a principle used in the basis of the silicone industry. Additionally, the performing of the hydrolytic condensation of dimethyldichlorsilane resulted in a silicone oil product which eventually reacted with boric acid. The boric acid in this reaction acts as the crosslink. Depending on the weight percentage used (3% or 12%) and whether or not calcium carbonate was added as a filler, different products are obtained. To determine the purity of the silicone oil, an IR spectrum was utilized. Additionally, an IR spectrum was obtained for the aged silicone oil as well.
Procedures:
Procedures were followed as outlined in the lab manual. 107L_S18_POL_lab_manual
Results:
I. Part I: Preparation of the Ziegler-Natta Catalyst for Ethylene Polymerization
nH2C=CH2 +TiCl4 + AlEt3 (H2C-CH2)n
Compound
Molar Mass
Amount Obtained
Moles
Melting point
Equivalents
Observation
Theoretical Yield
% Yield
Polyethylene
Range: 200 -1500
0.176 g
N/A mass varies
204 oC
1:1
Yellow / white solid flakes
0.99 g
17.8 %
Table 1: Stoichiometry of Ethylene polymerization
II. Part II: Hydrolytic Condensation of Dichlorodimethylsilane
Me2SiCl2 + 2H2O Me2Si(OH)2 + 2HCl
Compound
Molar Mass
Amount Obtained
Moles
Melting point
Equivalents
Observation
Theoretical Yield
% Yield
Silicone Oil
162.379 g/mol
0.744 g
0.00458 moles
-50 oC
1:1
Colorless oil solution
3.071 g
24.2 %
Table 2: Stoichiometry of Dichlorodimethylsilane
Figure 1: IR Spectra for original (non-aged) Silicone Oil
Figure 2: IR Spectra for aged Silicone Oil
Functional group
Peak / Frequency (cm-1)
Si-R / R-Si-R stretch (broad)
800.46
Si-OR stretch (broad)
˜ 1110
Si-CH3 stretch (sharp)
1261.45, ˜ 1410
sp3 C-H stretching (sharp)
2962.66
Table 3: IR spectrum analysis
Test tube
Silicone oil mass
Boric acid mass
Calcium Carbonate Mass
Mass obtained
Physical appearance
3%
0.248 g
0.0074 g
0.00496 g
0.24 g
White goo /silly putty, easy to pull apart
12%
0.19 g
0.022 g
0.0036 g
0.19 g
White crystals
Table 4: Test Tube observation with Calcium Carbonate
Test tube
Mass before heating
Mass obtained
Physical appearance
3%
0.36 g
0.177 g
Held shape, tougher than 12%, bounces with no stretch
12%
0.56 g
0.423 g
Colorless, no bounce, flows in middle, clear
Table 5: Test tubes without filler (Calcium Carbonate)
*Data from classmates as their observation for comparison therefore, don’t have complete data of amount of silicone oil mass and boric acid mass was in each test tube.
Discussion:
I. Part I: Preparation of the Ziegler-Natta Catalyst for Ethylene Polymerization
To begin this week’s experiment, all glassware was initially removed from a drying oven, allowing for the drying of all water remaining on the glassware. Eventually, the glassware was transferred into a glovebox, therefore the drying of the glassware was critical beforehand. But, before the transferring into the glovebox itself, the glassware was placed in an antechamber for forty-five plus minutes. This allowed for all the air present in the antechamber to be removed. If there was water remaining on the glassware, a corrosive HCl would have been produced by the reacting of TiCl4 with H2O. In addition, if the antechamber was not vacuumed air free, the triethylaluminum compound would ignite spontaneously as it becomes exposed to O2. Therefore, the addition of TiCl4(THF)2, AlEt3, and dry hexane was mixed in a Schlenk flask, in the glovebox.
The transition metal, titanium, contains one empty orbital in the 4s orbital and five in the 3d orbitals, for a total of six empty orbitals. To stabilize, titanium is able to arrange its structures in order for each titanium atom to coordinate with the six chlorine atoms. However, eventually the titanium atom will only contain four chlorine atoms. An octahedral geometry is eventually formed from the Titanium atom. During the chain initiation step (Figure 3), addition of AlEt3 to TiCl4, one CH2CH3 group is donated, forming the metal alkyl complex. During the forming of the metal alkyl complex, the color of the solution turned from a light yellow/clear color to a dark blue colored solution.
Figure 3: Chain initiation step for the addition of AlEt3
Furthermore, the chain propagation step involved the addition of a double bonded ethylene with the metal alkyl complex formed in figure 3. The addition of the metal alkyl complex with ethylene helped to form a metal-olefin complex (Figure 4).
Figure 4: Chain propagation step for the forming of a metal-olefin complex
During the chain propagation step, two π electrons fill the empty orbital for the Titanium atom. The chain propagation allows for the creation of a longer (CH2CH3)n chain. The electrons are eventually transferred through chain transfer.
During chain transfer, a metal-hydride complex was formed. The chain transfer step occurred through the elimination of a β-hydrogen. Eventually, a metal-alkyl complex was formed again by adding ethylene. However, the metal-alkyl complex contained an H atom at the end of the molecule in comparison to that in figure 4.
Ultimately, a polyethylene solid was filtered and obtained. The product was observed to be a light yellow with white flakes. Post wash with acetone, the melting point for the compound was determined to be 204 oC. However, experimental value for the melting point is unusually much greater than the theoretical value of 135 oC. This is partly due to the compound being impure. Because the compound had such a high melting point, it can also be assumed that the density of the product was much greater than expected.
Part II: Hydrolytic Condensation of Dichlorodimethylsilane
For part two of the experiment, a condensation reaction was performed to produce a dimethylsilanediol polymer. In order to slow the rate and allow Si(CH3)2(OH)2 to polymerize, the reaction was performed in an ice bath. As dimethyldichlorosilane, Me2SiCl2, reacts with H2O, dimethylsilanediol, Me2Si(OH)2, is formed. In addition to the forming of Me2Si(OH)2, two HCl by products are formed as well (Figure 5).
Figure 5: Reaction for the forming of dimethylsilanediol and 2 HCl byproducts
As Me2Si(OH)2 is condensed, an H2O byproduct forms as well. The linear chain oligomer forms through the continual process of the intermolecular condensation. Moreover, an Erlenmeyer flask was used to separate the ether and water layers. Because the density of water is greater than that of ether, the water was at the bottom of the Erlenmeyer flask, while the ether layer was on the top. Just to clarify, the water technique learned in organic chemistry lab was utilized. In order to neutralize the corrosive HCl, NaHCO3 was added. To dry the ether solution, MgSO4 was used, absorbing the water molecules. MgSO4 was then was easily removed by gravity filtration based on its insolubilty.
The final product, dimethylsilanediol, Me2Si(OH)2, was a colorless oil solution. The percent yield for the product obtained was determined to be 24.2 %. The low percent yield was partly due to the limited amount of time available to produce the chain.
Based on the IR spectra, the purity of the silicone oil was determined through an in-depth analysis (table 3). In comparison to the aged silicone oil, the aged silicone oil had a higher percent transmittance because the growth of the chain proceeds for a longer period of time.
Furthermore, the remaining silicone oil was evenly distributed into two different test tubes, 3% and 12%, to investigate the crosslinking of boric oxide and silicone oil. Half of the lab groups added a filler to the test tube, calcium carbonate. The mixture of the two test tubes were heated in a sand bath at 200 oC for two hours. Ultimately, a putty goo was produced by the crosslinking process altering the polymer properties. The test tubes were eventually removed after two hours in heat for comparison. The product obtained from the 3% was visualized as a white product similar to that of the 12% test tube, however, the product from the 12% test tube seemed to be firmer forming crystals.
Conclusion:
As the coordination polymerization of ethylene was performed, through the use of a glovebox, the synthesis of polymers was observed. A hydrolytic condensation polymerization of Me2SiCl2 was carried out for Part II. The melting point for the polyethylene compound was unusually high. High density was a possible indication for such a high boiling point. The percent yield obtained for the silicone oil was 24.2 %. Moreover, the IR spectra indicated a fairly pure compound for the silicone oil, with % transmittance being higher for the aged silicone oil. In correspondence to the silicone oil, boric acid acts a crosslink forming a colorless/white putty goo, depending on the weight percentage used. Overall, this experiment helped to obtain a better understanding and gain experience working with air sensitive materials. Therefore, it is important to remember, when dealing with air sensitive compounds, to be proficient and understanding of the inorganic compounds, as they are capable of igniting at any given time if exposed to air.
Reference:
Law, Matt “107L_S18_POL_lab_manual” Writing lab. PDF, April 24, 2018
Law, Matt “107_S18_Glovebox_Techniques. April 16, 2018
Post Lab Questions:
1. 100-mer of ethylene balanced equation: 100(H2C=CH2) +TiCl4 + AlEt3 + ClAlEt2 *where n in products is = 100 Chain termination: TiCl4 + AlEt3 Cl3TiEt + ClAlEt2 Cl3TiEt + H2C=CH2 Cl3Ti(CH2CH2)nH Hydrolytic condensation of dichlorodimethylsilane balanced equation: 20 SiMe2Cl2 •20H2O + 40 HCl *where n = 20 in product
2. Concentrated HCl (Polyethylene) Ethyl Chloride synthesis: HCl + CH3CH2OH CH3CH2Cl + H2O Cl3Ti(CH2CH2)n CH2CH5 + CH3CH2Cl → TiCl4 + C2H5(CH2CH2)nCH2CH5 Ethyl chloride is produced from the 1:1 mixture of concentrated HCl and ethanol, to remove titanium from the chain of polyethylene, terminating the growth. Concentrated sodium bicarbonate (silicone oil) HCl + NaHCO3 → NaCl + H2O + CO2 Me2SiCl2 + H2O → Me2Si(OH)2 + 2HCl
Ultimately, the goal was to neutralize the corrosive HCl. Therefore, bicarbonate is added, removing the acid.
3. Original: Aged:
Functional group
Peak / Frequency (cm-1)
Si-R / R-Si-R stretch (broad)
800.46
Si-OR stretch (broad)
≈ 1110
Si-CH3 stretch (sharp)
1261.45, ≈ 1410
sp3 C-H stretching (sharp)
2962.66
In comparison, the IR spectra for the aged silicone oil revealed a higher percent transmittance, because the chain grew for a longer period of time. Additionally, the peaks tend to be sharper, especially for the Si-O-Si stretch, as the aged silicone oil does not have as large of a broad peak.
4. ∆G° = ∆H -T∆S (Gibbs free energy) ∆H= -22.7 kcal/mol; ∆S= -0.0239 kcal/mol•K ∆G° must be positive ∆H = ∆S at ceiling temperature T = ∆H / ∆S = (-22.7 kcal/mol / -0.0239 kcal/mol•K) = 949.8 K ≈ 677 oC Due to the high temperature, 950 K, the reaction is thermodynamically favored, hence why the polymer is able to depolymerize.
5. The required glassware is heated and dried in a drying oven in order to eliminate any remaining H2O that can potentially condense. The elimination of H2O from all glassware prior to being transferred into a glovebox is crucial because, a corrosive HCl can be produced if H2O and TiCl4 were to react together or any other sensitive reagents.