When we do esterfication using alcohol with acid, i have a question for reactivity of two diols.
diethylene glycol and polyethylene glycol200.
Is there any difference of reactivity of two diols? (Ex. Electrophilicity of oxygen of hydroxyl)
Ethylene glycol may need longer time and Dean-Stark trap for the esterification. Give enough time and make sure you use excess carboxylic acid to make the diester.
However, for the polyethylene glycol (PEG) is the polymeric form of ethylene glycol. So, it may have only the terminal hydroxyl group. Depending on the size of the PEG linker you are trying to use here, you may need to optimize the reaction. Can you provide more inforMarion about what kind of PEG ester you are trying to synthesize?
As in the esterification process, the O-H bond of alcohol is to be broken and the -OH bond of acid is to be broken for the ester to be formed, so we have to compare the accessibility and ease of breaking of O-H bonds of both alcohols. Both DEG and PEG have two O-H bonds available/molecule for breaking. But DEG is smaller in size (having 4 carbon atoms only) than PEG200 molecule (on average, has 8-9 carbon atoms), thus the DEG molecule suffers less steric hindrance for approaching the bonding site of the acid. The DEG molecule also is less heavy (as it has a smaller molar mass) than the PEG200 molecule. As viscosity values are comparable for both alcohols, so small-sized and less heavy DEG molecules can easily manipulate their positions in the acid + alcohol mixture to make the esterification reaction go faster as compared to PEG200 molecules' position manipulation. Thus the reactivity of DEG is expected to be more as compared to PEG200's reactivity in the esterification process.
Explanation Supporting data
Diethylene glycol (DEG) :
Chemical Formula : C4H10O3 , Molar Mass = 106.12 g/mol, Viscosity = 35.7 cP, Density = 1.118 g/ml, DEG is a colorless, low-volatility, low viscosity, hygroscopic liquid.
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Polyethylene glycol -200 (PEG200) :
Chemical Formula : C2nH4n+2On+1 , n = 4.14 for PEG200
Molar Mass = 44.05n + 18.02 g/mol = 200g/ml, density = 1.125 g/ml
PEG is a hydrophilic molecule. a water-soluble polymer,. It is Clear, Colorless Liquid at 25 deg C.
Most carboxylic acids are suitable for the reaction, but the alcohol should generally be primary or secondary. Tertiary alcohols are prone to elimination.
Most reactive alcohol towards esterification is primary alcohol. As the size of group R around ⎯OH increases, the rate of esterification reaction decreases due to steric hindrance.
The kinetics of the reaction between a carboxylic acid with either diethylene glycol or any polyetheylene glycol are the same. "Viscosity" has absolutely nothing to do with kinetics.
Devinder Pal Singh what is meant by 44.05n, here what is n? Molar Mass = 44.05n + 18.02 g/mol = 200g/ml
1. why does PEG have different molecular weights?
Immanuel Paulraj,
The molar mass of PEG is given by: Molar Mass = 44.05n + 18.02 g/mol, where n is the number of subunits. 44.05 g/mole is the molar mass of 1 subunit of PEG.
A subunit of PEG contains two carbon atoms, four hydrogen atoms and one oxygen atom. For PEG-5000, the number of subunits is n = 113.
Reference: Oesterhelt, F., Rief, M., Gaub, HE. Single-molecule force spectroscopy by AFM indicates the helical structure of polyethylene glycol) in water. New Journal of Physics. 1999;1(1):6.
Different samples of PEG have different molecular masses (or weights), as these samples contain different numbers of subunits of PEG.
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