HCl salt form

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Pharmaceutical drugs are often listed as being provided in HCl salt form. These drugs have HCl added to increase the drug solubility by:

A. protonating a carboxyl group
B. dehydrating an alcohol
C. protonating an amine group
D. hydrogenating an alkene group


How does someone attack such question? I am going to fail that test....

B? HCl has a pKa below COOH and NH3 so both would get protonated; A and C don't make sense. Increasing solubility in tissues means making something non-polar so it is fat soluble. Alkenes are already nonpolar and I'm pretty sure you hydrogenate alkenes with H2+metal catalyst (like Pt). So B seems to make sense. Dehydrate an alcohol = make the alcohol less polar = more soluble through the membrane.

Originally Posted by MedPR

B? HCl has a pKa below COOH and NH3 so both would get protonated; A and C don't make sense. Increasing solubility in tissues means making something non-polar so it is fat soluble. Alkenes are already nonpolar and I'm pretty sure you hydrogenate alkenes with H2+metal catalyst (like Pt). So B seems to make sense. Dehydrate an alcohol = make the alcohol less polar = more soluble through the membrane.

It's C...
Solubility of organic compounds can be most easily increased by protonation/deprotonation of groups to cause them to become charged. This forms salts which are far more soluble in water than uncharged molecules. Since HCl is being added to the drug, this is a protonation event. Protonation of an amine would cause it to become an ammonium cation which is soluble in water. Carboxyl groups and alcohols can have their solubilities increased by deprotonation rather than protonation.

Originally Posted by Temperature101

Pharmaceutical drugs are often listed as being provided in HCl salt form. These drugs have HCl added to increase the drug solubility by:

A. protonating a carboxyl group
B. dehydrating an alcohol
C. protonating an amine group
D. hydrogenating an alkene group


How does someone attack such question? I am going to fail that test....

C?
Is that from MCAT Q of the day? I just answered it
Remember the goal of this reaction is to make the drug more soluble.

A not very likely since carboxyl group is already protonated
B that would not make the drug more soluble
D is obviously wrong since HCl would not result in hydrogenation.

Interesting. I guess you have to know that charged = more soluble?

Originally Posted by MedPR

Interesting. I guess you have to know that charged = more soluble?

I think this would apply to polar solvents, like water.
But now that you brought up tissues may be the question should have been a little more explicit what were they referring to when talking about solubility.

Originally Posted by pm1

I think this would apply to polar solvents, like water.
But now that you brought up tissues may be the question should have been a little more explicit what were they referring to when talking about solubility.

Yea that's true. I mean I certainly see how more charge would make it more soluble in water, but I immediately thought solubility in tissues. Oh well, tough question.

Originally Posted by Temperature101

Pharmaceutical drugs are often listed as being provided in HCl salt form. These drugs have HCl added to increase the drug solubility by:

A. protonating a carboxyl group
B. dehydrating an alcohol
C. protonating an amine group
D. hydrogenating an alkene group


How does someone attack such question? I am going to fail that test....

Drug questions in Bio almost always focus on absorption. When you see questions like this, think digestion/absorption.