Name: Urker Abibulla
Date Performed: 01.09.2023
Experiment No. 1
Title of Experiment: Preparation of Tri-n-propyl borate
I.
INTRODUCTION
The objectives of the experiment are: to conduct synthesis of tri-n-propyl borate; to
calculate the % yield of the product; to obtain and analyze IR and H-NMR spectrums of the
product; and to determine possible sources of error.
Theory. Trialkoxyboranes such as tri-n-propyl borate are widely used in several fields such
as the glass industry, biochemistry, photography, and polymer chemistry [1]. These
chemical compounds are popular because of their air stability. The B-O bond expresses high
stability due to the compatibility of oxygen’s electron lone pairs with the empty π orbital of
borane. This B-O bond appears at 1300-1500 cm-1 and O-C at around 1000 cm-1 [2]. At 1HNMR, alkane groups (C-CH2-C) appear at 0.5ppm-2ppm, and the HC-O appears at around
4ppm. At the 11B-NMR spectrum, trialkoxyboranes appear at 10-20ppm [3].
In this experiment. A dehydration reaction occurs when the hydrogen of the acid removes
the hydroxy group of n-propanol. So, water forms as a byproduct. Toluene is used together
with water as an azeotrope to convey it to the side arm. The product is separated from water
and toluene using heating with Hickman still and a water condenser. When reflux is
established, the evaporated mixture is collected in the still’s collar. The used apparatus is
illustrated in Figure 1. The reaction equation:
B(OH)3 + 3C3H7OH
B(OC3H7)3 + 3H2O (1)
Figure 1. The reaction apparatus setup.
Figure 2. Structure of tri-n-propyl borate.
II.
CHEMICALS.
All reagents of laboratory work are shown in Table 1 below.
Table 1. Physical-chemical properties of reagents
Compound
MM, M.P., b.p.,
Density, Solubility
g/mL at
g/mol (°C)
°C
20°C
Boric acid
61.83 170300
1.44
4.72 g/100
171
mL (20 °C)
n-propanol
60.09 -127
97
2.07
miscible
52
Flammability Toxicity/
hazards
Nonflammable
Highly
flammable
irritant; toxic,
corrosive [4]
Irritant. toxic
[5]
Toluene
92.14
95
110111
0.865
-
Highly
flammable
Irritant. toxic
[6]
Tri-n-propyl
borate
188.0
74
-
175177
0.815
Soluble in
organic
solvents
flammable
Irritant [7]
III.
PROCEDURE
A 50mL round bottom flask with a boiling chip was weighed (40.2527 g). 1.00287 g of
boric acid was transferred into the 50 mL round bottom flask with a boiling chip. After,
2mL of toluene and 4 mL of n-propanol were added. Hickman still with the water condenser
was set with the flask. The whole apparatus was placed over a hot plate inclined. The
mixture was heated until the reflux was reached. Water and toluene collected in the sidearm
of the still were transferred by pipette. The flask was heated until 120°C when the water
stopped collecting in the sidearm. After the temperature reached 120°C, the flask was
cooled to room temperature. The product that was left in the flask was weighed and the
%yield was calculated. Finally, the IR spectrum of the product was obtained and analyzed.
H-NMR of tri-n-propyl borate was provided.
IV.
RESULTS & DISCUSSION
Table 2. The results of the experiment
The mass of boric acid
The molecular mass of boric acid
The mole of boric acid
The volume of n-propanol
The density of n-propanol
The molecular mass of n-propanol
The mole of n-propanol
Theoretical mass of the product
Experimental mass of the product
% yield of the experiment
1.00287 g
61.83 g/mol
0.01622 mol
4 mL
2.07 g/mL
60.0952 g/mol
0.13778 mol
3.05056 g
0.853 g
27.96%
𝑛=
𝑚
𝑀
𝑉∗𝑑
𝑛=
𝑀
𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡𝑎𝑙 𝑚𝑎𝑠𝑠
%𝑦𝑖𝑒𝑙𝑑 =
∗ 100%
𝑡ℎ𝑒𝑜𝑟𝑖𝑡𝑖𝑐𝑎𝑙 𝑚𝑎𝑠𝑠
(1)
(2)
(3)
The theoretical mass was calculated using the mole of deficient reagent (boric acid) and
Formula 1. The % yield of the experiment was calculated using Formula 3 and is 27.96%,
which is very low. This may be due to several reasons. Firstly, the flask was heated at 500°C,
because the digit of temperature on the thermometer inside the Hickman still didn’t reach 120°C
but the solution’s temperature was over 200°C and maybe a significant part of the product was
transferred to the sidearm, and removed with water and toluene. Secondly, some amount of the
product was accidentally disposed of before weighing. Thirdly, some amount of reagent was
lost in dishes while transferring. The IR spectrum of the product displays several peaks. B-O
strong bond peak between 1300-1500 cm-1, O ̶ C at 1081.62 cm-1. There is a small smooth peak
at 3442.74 cm-1 that shows the presence of water, but this amount can be neglected and the
product can be considered as pure enough. Peaks at 2879.45 cm-1 and 2965.77 cm-1 are C-H
bonds. Analyzing, the 1H-NMR spectrum: first peak is triplet at 0.9 ppm, (-C-CH3)3 protons
with the highest intensity and number of protons (9H), second peak is multiplet at 1.5-1.65 ppm,
(-C-CH2-C)3 (6H), third peak is triplet at 3.7-3.9, (-O-CH2-C)3 (6H), small fourth peak at
7.25ppm is singlet. Indicates the aromatic compound of toluene. At the 11B-NMR spectrum, the
B-O bond appears at 15-20 ppm. These values correspond with literature values. So, analysis
with IR and NMR shows that reaction went successfully and product obtained, but contain some
amount of impurities such as water and toluene.
Figure 3. 1H-NMR spectrum of tri-n-propyl borate.
Figure 4. 11B-NMR spectrum of tri-n-propyl borate.
Figure 5. IR spectrum of the obtained product.
Figure 5. IR spectrum of the tri-n-propyl borate literature [2].
V.
CONCLUSION
In this experiment, we have synthesized tri-n-propyl borate from boric acid and n-propanol.
The % yield was calculated (27.96%). The IR spectrum of the product was analyzed and
compared with tri-n-propyl borate. A small portion of water was noticed in the IR spectrum,
but this amount can be neglected. The frequency of the B ̶ O (between 1300-1500 cm-1) and
O ̶ C (1081.62 cm-1) bonds were identified. The sources of error and impurity were
considered. All objectives were achieved.
Post-lab questions:
Borates are extensively used in the glassmaking industry, as are silicates and aluminates.
Perform a literature search and describe the use of these materials in the manufacture of
glass. What attractive properties do they confer on the glass?
Borates enhance durability, glass’s mechanical strength, and resistance to chemical
reactions, thermal stress, water, and scratches required in current applications. Boric oxide
reduces glass's melting temperature and viscosity, prevents glass from crystallizing,
regulates thermal expansion, and prevents devitrification. Borates are stable due to the
compatibility of oxygen’s electron lone pairs with the empty π orbital of borane [8].
Reference
1. Szafran, Zvi; Pike, Ronald M.; Singh, Mono M., Microscale Inorganic Chemistry: A
Comprehensive Laboratory Experience;1stEd.; J. Wiley: 1991; pp. 248-251
2. Pouchert, C., Ed., Aldrich Library of FT-IR Spectra, Aldrich Chemical Co.: Milwaukee,
WI, Vol. II, pp. 1132 C
3. Pouchert, C., Ed., Aldrich Library of NMR Spectra, Aldrich Chemical Co.: Milwaukee,
WI, Vol. III, pp. 725 B
4. Material Safety Data Sheet for boric acid. Retrieved from:
https://www.fishersci.com/msds?productName=AC315181000
5. Material Safety Data Sheet for propanol. Retrieved from:
https://www.fishersci.com/store/msds?partNumber=A414500&productDescription=1PR
OPANOL+CERTIFIED+500ML&vendorId=VN00033897&countryCode=US&languag
e=en
6. Material Safety Data Sheet for toluene. Retrieved from: https://betastatic.fishersci.com/content/dam/fishersci/en_US/documents/programs/education/regulat
ory-documents/sds/chemicals/chemicals-t/S25611.pdf
7. Material Safety Data Sheet for tri-n-propyl borate. Retrieved from:
https://www.fishersci.ca/shop/products/tri-n-propyl-borate-98-thermo-scientific/p7049808
8. “Borates in Glass Manufacturing: Unbreakable Benefits, Unbeatable Versatility.”
BoraxCorp, www.borax.com/news-events/october-2019/borates-in-glass-manufacturing.
Accessed 12 Sept. 2023.