Why is dichloromethane a good organic solvent?

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Discussion Overview

The discussion revolves around the properties of dichloromethane (DCM) as an organic solvent, particularly its miscibility with alcohols compared to water, and its overall effectiveness in various applications. Participants explore the polarity of DCM, its density, and its interactions with other substances in the context of chemistry labs.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants note that both water and dichloromethane are polar molecules, yet DCM mixes better with alcohols than water does, prompting questions about the reasons for this difference in miscibility.
  • One participant suggests that DCM is less polar than water, which may explain its better miscibility with organic compounds, particularly higher weight alcohols.
  • Another participant provides a comparison of the electronegativity differences in C-Cl and C-H bonds, arguing that DCM is barely polar and much less polar than water.
  • It is mentioned that DCM's density makes it advantageous for use in separatory funnels during aqueous workups, as it will settle at the bottom due to being denser than water.
  • Concerns are raised about the toxicity of DCM, although it is noted to be the least toxic among chlorinated ethers, and its diffusivity in water is highlighted as being higher than that of water in DCM.
  • One participant points out that DCM is generally a good solvent for hydrophobic polymers, specifically mentioning its effectiveness for polylactic acid (PLA).

Areas of Agreement / Disagreement

Participants express varying views on the polarity of dichloromethane and its implications for miscibility and solvent effectiveness. There is no consensus on the extent of its polarity or the implications for its use as a solvent.

Contextual Notes

Participants discuss the miscibility of DCM with different alcohols, particularly noting the distinction between higher weight alcohols and smaller ones like methanol and ethanol. The discussion also touches on the toxicity of DCM and its practical applications in laboratory settings.

birdstudyphys
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I was working on my chem lab, this question occurred to me. Water and dichloromethane are both polar molecule. However, dichloromethane is able to mix with alcohols much better than water. Is there a polarity difference that caused the miscibility to be different?
 
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birdstudyphys said:
I was working on my chem lab, this question occurred to me. Water and dichloromethane are both polar molecule. However, dichloromethane is able to mix with alcohols much better than water. Is there a polarity difference that caused the miscibility to be different?
Of course you are talking about higher weight alcohols, not CH3OH or C2H5OH, which are completely miscible with water. However CH2Cl2 is not as polar as water so it mix better than water with organic compounds.
 
Yeh. CH2Cl2 is barely polar actually since C-Cl has deltaEN=0.5 where C-H gives a 0.4.
Much less polar than water for sure.. Well that explains it. Thanks. I was totally misled by my weird thinking... Egrrr.
 
DCM is also an excellent solvent for convenient reasons like being more dense than water so it will be on the bottom in a separatory funnel if you do an aqueous workup and it is also easy to evaporate.
 
However it is toxic, though the least of the chlorinated ethers. CH2Cl2 is partially miscible in water (it is not polar) , but its diffusivity in water is higher that water in CH2Cl2. IF working with hydrophobic polymers, it tends to be in general a good solvent. Specially for PLA.
 

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