pKa of SDS

[Louis Hom]

Does anyone know the pKa of SDS (sodium dodecyl sulfate)? I'm guessing
it's near 2 (the 2nd pKa of H2SO4), but don't know for sure.
--
_______________________________________________________________________________
Lou Hom >K '93
lh...@nature.berkeley.edu No method to my madness.
http://www.ocf.berkeley.edu/~lhom

[wo...@mmad1.pmmp.uic.edu]

Isn't SDS "sodium dodecyl sulfonate" and not "sodium dodecyl sulfate"?

[Ron Tate]

No it's "sulfate"
--
>>>>>>--------------------------->
>Ron Tate
>Lab of Franklin Leach
>Dept. of Biochem. & Molecular Biology
>Oklahoma State University rt...@bmb-fs1.biochem.okstate.edu
(405) 744-9326
---------------------------------------------

[wo...@mmad1.pmmp.uic.edu]

Ron Tate wrote:
>
> wo...@mmad1.pmmp.uic.edu wrote:
> >
> > Louis Hom wrote:
> > >
> > > Does anyone know the pKa of SDS (sodium dodecyl sulfate)? I'm guessing
> > > it's near 2 (the 2nd pKa of H2SO4), but don't know for sure.
> > > --
> > > _______________________________________________________________________________
> > > Lou Hom >K '93
> > > lh...@nature.berkeley.edu No method to my madness.
> > > http://www.ocf.berkeley.edu/~lhom
> >
> > Isn't SDS "sodium dodecyl sulfonate" and not "sodium dodecyl sulfate"?
>
> No it's "sulfate"
> --

I coulda sworn it was an ester of a sulfonic acid, not of sulfuric acid

[Jennifer Blanc]

Sulfuric acid. AKA sodium lauryl sulfate (as found on shampoo bottles).
As for the pKa, you'd have to check out the Sigma/Aldrich catalog
(usually has this info) or maybe the Merck index. It's not in the CRC.

-JBlanc
"future under construction"

[Andy Phillips]

wo...@mmad1.pmmp.uic.edu wrote:
>
> Louis Hom wrote:
> >
> > Does anyone know the pKa of SDS (sodium dodecyl sulfate)? I'm guessing
> > it's near 2 (the 2nd pKa of H2SO4), but don't know for sure.
> > --
> > _______________________________________________________________________________
> > Lou Hom >K '93
> > lh...@nature.berkeley.edu No method to my madness.
> > http://www.ocf.berkeley.edu/~lhom
>
> Isn't SDS "sodium dodecyl sulfonate" and not "sodium dodecyl sulfate"?

No

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[Torsten Boerchers]

Its indeed an ester between sulfuric acid and laurylalcohol and
thus called lauryl(or sodiumdodecyl)sulfate
Look e.g. in the Sigma catalogue to see the composition.

Regards
Torsten

wo...@mmad1.pmmp.uic.edu wrote:

snip

>> > > Lou Hom >K '93
>> > > lh...@nature.berkeley.edu No method to my madness.
>> > > http://www.ocf.berkeley.edu/~lhom
>> >
>> > Isn't SDS "sodium dodecyl sulfonate" and not "sodium dodecyl sulfate"?
>>

[Gene Huh]

In article <4l4jit$5...@agate.berkeley.edu>, lh...@nature.berkeley.edu
(Louis Hom) wrote:

> Does anyone know the pKa of SDS (sodium dodecyl sulfate)? I'm guessing
> it's near 2 (the 2nd pKa of H2SO4), but don't know for sure.
> --
>
_______________________________________________________________________________

> Lou Hom >K '93
> lh...@nature.berkeley.edu No method to my madness.
> http://www.ocf.berkeley.edu/~lhom

To address your original question (rather than debate its chemical
structure :), I would guess that it's closer to the first pKa rather than
the second, since the dodecyl sulfate ion is only singly charged (and
therefore more like HSO4- than SO4--).
Gene Huh
gs...@garnet.berkeley.edu

[wo...@mmad1.pmmp.uic.edu]

So you guys think BOTH pka's of SDS are less than zero? I think not!

[Dr John Christie]

In article <317D4F...@mmad1.pmmp.uic.edu>, wo...@mmad1.pmmp.uic.edu wrote:

< So you guys think BOTH pka's of SDS are less than zero? I think not!

SDS - sodium dodecyl sulfate - strictly contains **NO** acidic protons,
and so cannot have a pKa.

C12H25OSO3- Na+

Its conjugate acid - dodecylsulfuric acid - is a strong acid which
dissociates completely in water, so pKa is not a useful concept, but its
**ONE** pKa is clearly less than zero.

C12H25OSO3H

The reference to **BOTH** pKa s can only be referring to some other
substance, or based on a complete misunderstanding of the structure of the
material.

John

[esm...@ncsu.edu]

I am currently taking Biochemistry. In my biochem text book it depicts sodium dodecyl sulfate as a sulfur surrounded by 4 oxygens and a 12 hydrocarbon long chain coming off of one of the oxygens. There are double bonds between 2 of the oxygens and single bonds between the other 2. Thus it has a charge of -1. It doesn't say anything about the pKa. We had a quiz today in class where we had to draw this molecule at a pH of 7. I think this was some sort of trick question. It's called sulfate, so wouldn't it always be de-protonated, regardless of the solution's pH?
Additionally, what Dr. John Christie said lends evidence to this. "SDS dissociates completely in water..." so it will always be missing it's proton in any solution right? Please correct me if I'm thinking about this wrong. Thanks.

[Poutnik]

esm...@ncsu.edu posted Wed, 5 Feb 2014 21:04:41 -0800 (PST)

> Additionally, what Dr. John Christie said lends evidence to this. "SDS
> dissociates completely in water..." so it will always be missing it's
> proton in any solution right? Please correct me if I'm thinking about
> this wrong. Thanks.
>

SDS is in half an ester of alcohol and sulphuric acid = no pKa,
in the other half alkaline salt of the same acid = no pKa.

I do not take into account very low pKa
of hydrocarbon hydrogen at esteric alpha carbon atom.

There is sense of speaking pKa of DS acid
and conjugated pKb of SDS
pKa + pKb = 14 / 25 deg C



--
Poutnik

[Norm X]

>> Additionally, what Dr. John Christie said lends evidence to this. "SDS
>> dissociates completely in water..." so it will always be missing it's
>> proton in any solution right? Please correct me if I'm thinking about
>> this wrong. Thanks.

Yes, sodium dodecyl sulphate does dissociate completely in water and the
sodium cations have no propensity to aggregate. However, the fundamental
issue about the usefullness of SDS is its tendency to form micelles above
the critical micelle concentration. If you look at the structure of micelles
you see little spheroids, with the aliphatic tails pointing inwards and the
sulphate anions on the surface pointing outwards. At this point you need to
worry about the structure of water at the SDS micelle surface and the charge
energy of the surface. Some of that charge energy needs to be reduced by
protonation. Look up the titration curve for a weak triprotic acid like
citric acid. Then look up the size of the SDS micelle and count the number
of sulphate groups. I honestly cannot do the math nor care to look up what
you need to know but I know you are not close to the correct answer.

[Soviet_Mario]

Il 18/02/2014 01.54, Norm X ha scritto:
>>> Additionally, what Dr. John Christie said lends evidence to this. "SDS
>>> dissociates completely in water..." so it will always be missing it's
>>> proton in any solution right? Please correct me if I'm thinking about
>>> this wrong. Thanks.
>
> Yes, sodium dodecyl sulphate does dissociate completely in water and the
> sodium cations have no propensity to aggregate. However, the fundamental
> issue about the usefullness of SDS is its tendency to form micelles above
> the critical micelle concentration. If you look at the structure of micelles
> you see little spheroids, with the aliphatic tails pointing inwards and the
> sulphate anions on the surface pointing outwards. At this point you need to
> worry about the structure of water at the SDS micelle surface and the charge
> energy of the surface. Some of that charge energy needs to be reduced by
> protonation.

a tightly bound closer sphere of solvation could be enough,
for a strong electrolite

> Look up the titration curve for a weak triprotic acid like

I don't very much agree.
Normally in polyprotic acids the various Ka1, Ka2, ..., Kan
decrease for two independent factors.
* A statistical advantage for the first (of many) protons
removed, statistical disadvantage for the last (of the few
remaining) protons removed
* an intrinsical (including electronic effects, field
effects, inductive effects) more or sharp decrease.

In citric acid the second effect overwhelms statistical
considerations.

In your micelles just the statistical effect still holds.

I'm not sure it could be entirely neglected, perhaps not,
but i guess it is a feeble effect (in a ordinary soap
micelle, like sodium stearate or palmitate, all this is no
more true, for every single function is in itself a week
acid, so shows some hydrolisis even when alone)

> citric acid. Then look up the size of the SDS micelle and count the number
> of sulphate groups. I honestly cannot do the math nor care to look up what

neither can I. To make a very rough estimation of the
fraction of protonated R-O-SO3(-) changing pH of medium,
one could simply cutoff the highest edge, statinc that that
fraction is alike to the ratio of the two pKa of,
respectively, R-O-SO3-H and H3O(+).
The first should be somewhere in the range -6 / -7 (due to
high similarity to H2SO4), the second is assumed -1,75.
Beeing pessimistic, let assume -2 for hydroxonium.

Then there would be one millionth or a tenth of a millionth
of sulfonate group protonated. I ignore the average number
for micellae, but in a very large micella some few proton
could be taken.
This is only a rough estimation, for it implies no
interaction and different solvation effects, but actually
there could be cooperative effects when the molecules are
tidy stacked side by side (i dont know if stabilizing or
stabilizing ... probably favoring proton uptake due to
unfavourable field effects in the highly densely charged
aggregate).
Every 3-4 Kcal (or KJ, i dont remember) of additional
stabilization of solvation of protonated form in the
aggregate, the ratio i depicted before would increase by a
factor of 10 (at constant T).
But details are well beyond my basic phis-chem abilities

> you need to know but I know you are not close to the correct answer.
>
>

--
1) Resistere, resistere, resistere.
2) Se tutti pagano le tasse, le tasse le pagano tutti
Soviet_Mario - (aka Gatto_Vizzato)

[Bob M]

Dont know for sure but based on its binding with higher molecular amines in dil sulphuric acid it may well be stronger than the first ionisation of sulphuric acid.

On a similar note my favourite esterification catalyst is toluene sulphonic acid
with methanol/ higher fatty acids and acetic/ glycols or glycerol it is rapid giving nice clean reactions with few extraneous products to screw up GLC results.
I suspect Toluene sulphonic acid might also be a stronger acid than sulphuric

[Soviet_Mario]

Il 02/03/2014 18.03, Bob M ha scritto:

Hi Bob

> Dont know for sure but based on its binding with higher molecular amines in dil sulphuric acid it may well be stronger than the first ionisation of sulphuric acid.

I do not understand this argumentation ... for s few reason

1) higher amines have also hydrophobic parts, so, all other
things being (eventually) equal, the long hydrocarbon chain
of SDS should have an extra (London's dispersion forces)
interaction that H2SO4 cannot benefit of

2) more in general, since when binding (within a leveling
medium like water is) is a proof of dissociation extent ?
For substances whose H° (Hammet acidity function) is in such
range as -2 to -10 or more, hence meaningless and non
measurable in water, where both acids have apparently
infinitive constants, all data relative to water are not
conclusive i think

>
> On a similar note my favourite esterification catalyst is toluene sulphonic acid
> with methanol/ higher fatty acids and acetic/ glycols or glycerol it is rapid giving nice clean reactions with few extraneous products to screw up GLC results.
> I suspect Toluene sulphonic acid might also be a stronger acid than sulphuric

uhm, it is not. I recall some 10-100 fold less.
Methanesulfonic is about the same.


But PTSA still has many advantages : it is more soluble in
organic solvents (also of low polarity), and it is a
negligibly OXIDIZING agent
(mesilic acid also is not oxidizing).

Let's also recall that neat H2SO4 (or even 98 % frequently
used) is not a pure substance, but contains appreciable
quantities of stronger acids (H3SO4+, H2S2O7 and fuming one
also H2S3O10), all of which is too strong in non leveling
environments, too oxidizing and carbocation-forming.

Polimeric moieties are absent in organic sulfonic acids,
that are always monomeric. So they are kinetically more
reliable. So PTSA is a better catalyst for Fischer than pure
H2SO4 (except for very robust substrates)

--------

Trifluoromethansulfonic (and fluorosulfuric) DO are stronger
than H2SO4 (i'm not sure of relative order, they should be
rather close). H° in the -12 / -13 range !
(HClO4 is extimated -10 for comparison)


I'm not sure also about so called nosylic acid (p-nitro
benzene sulfonic), which should be rather close to sulfuric
(yes still far from triflic and fluorosulfuric, in the
Olympo of acids, not to say Olah Magic acid, with its -15 H°)

Best Regards

[IV]

esmith wrote in
news:187118e3-11a8-4c17...@googlegroups.com...

Louis Hom wrote:
> Does anyone know the pKa of SDS (sodium dodecyl sulfate)?

Sodium dodecyl sulfate (SDS) is the sodium salt of dodecyl sulfuric acid.
Dodecyl sulfuric acid is a weak acid. If you draw the titration curve of the
titration of SDS with an acid, you get the pKa of the dodecyl sulfuric acid,
and the dependence between the concentration of SDS and pH. You can
calculate this titration curves by combining the laws of mass action of the
dissociation of SDS, dodecyl sulfuric acid and sodium hydroxide.

[IV]

"IV" wrote news:lfakra$5cf$1...@online.de...

> titration curve of the titration of SDS with an acid

Supplement: or the titration of dodecyl sulfuric acid with sodium hydroxide

[Soviet_Mario]

Il 06/03/2014 21.11, IV ha scritto:
> esmith wrote in
> news:187118e3-11a8-4c17...@googlegroups.com...
>
> Louis Hom wrote:
>> Does anyone know the pKa of SDS (sodium dodecyl sulfate)?
>
> Sodium dodecyl sulfate (SDS) is the sodium salt of dodecyl
> sulfuric acid. Dodecyl sulfuric acid is a weak acid.

which one do you consider as a reasonable threshold (in
terms of pKa) of a strong acid then ?
What pKa do you exteem for acids like R-O-SO2-OH ?

> If you
> draw the titration curve of the titration of SDS with an
> acid, you get the pKa of the dodecyl sulfuric acid, and the
> dependence between the concentration of SDS and pH. You can
> calculate this titration curves by combining the laws of
> mass action of the dissociation of SDS, dodecyl sulfuric
> acid and sodium hydroxide.
>
>

[IV]

"Soviet_Mario" schrieb im Newsbeitrag
news:lfaq5h$uj9$1...@speranza.aioe.org...

> Dodecyl sulfuric acid is a weak acid.
which one do you consider as a reasonable threshold (in
terms of pKa) of a strong acid then ?

O excuse me. I spoke here only in a conceptual system that knows only strong
acids and weak acids, not very strong, medium strong or very weak acids. My
"weak acid" only means that the dissociation of dodecyl sulfuric acid isn't
completely.
Substituion of sulfuric acid with a medium-chained or longer-chained alkyl
residue yields a weaker acid than sulfuric acid is.

> What pKa do you exteem for acids like R-O-SO2-OH ?

Maybe there is a group contribution method for calculating pKa of dodecyl
sulfuric acid. I will look in my literature next days.

[Soviet_Mario]

you could find a enlightening similarity considering the
series of partial esters of phosphoric acids

diesters (RO)2P(O)OH
monoesters (RO)P(O)(OH)2
free parent acid OP(OH)3

(and comparing only their first pKas).

In this series the strongest acid is the diester, the least
strong is the free acid (the monoester stays in the middle).
Many data can be found on charts from Bordwell university.

All are medium acids, not strong ones, but it is reasonable,
in an Hammett-like model of comparable susceptivities
("rho") and even more similar substituent effects ("sigma"),
that the same free energy linear relationship that holds for
fosforic acids holds for sulfuric series too.
The reaction is the same, and the two series are
structurally very similar.
The RO group actually shows a somewhat less effective
electron releasing effect than HO group.

so, at least in dilute solution and bulk interactions set
aside, the RO-SO2-OH should be prudentially considered not
weaker than HO-SO2-OH itself.
I dont want to extend this to conc. soln. or to pure
species, where eventual, stronger oligomers can be formed by
dehydration only for the free acid, and moreover the
H-bonding heavily influences the dissociation, solvating the
anions with different efficacy.
But in dilute soln. i exteem SDS in the rough range -7 to
-5,5 (corresponding to a truly strong acid, not a weak one)

[IV]

"IV" schrieb im Newsbeitrag news:lfd80g$qvv$1...@online.de...

German Wikipedia - Organische Säuren:
The monoesters of sulfuric acid and sulfonic acids have an acid strength
comparable to that of sulfuric acid. The +I effect of long alkyl chains
stabilizes the resulting anions.

pKa (25 °C)
---------------
sulfuric acid: −3
dodecyl sulfuric ester = lauryl sulfate = dodecyl sulfuric acid: −0,09*

*) Stahl, P. H.; Wermuth, C. G.: Handbook of Pharmaceutical Salts:
Properties, Selection, and Use. 2002, Helvetica Chimica Acta, ISBN
3-906390-26-8


That means: dodecyl sulfuric acid is a very strong acid, but a weaker acid
than sulfuric acid.

[Soviet_Mario]

Il 08/03/2014 20.59, IV ha scritto:
> "IV" schrieb im Newsbeitrag news:lfd80g$qvv$1...@online.de...
>
> German Wikipedia - Organische Säuren:
> The monoesters of sulfuric acid and sulfonic acids have an
> acid strength
> comparable to that of sulfuric acid. The +I effect of long
> alkyl chains
> stabilizes the resulting anions.
>
> pKa (25 °C)
> ---------------
> sulfuric acid: −3

Jerry March's Advanced Organic Chemistry reports -10

On Carey Sundbert (part A) there is a table with H°

% H2SO4 H° %H2SO4 H°
5 0 ,24 55 −3 91
10 −0, 31 60 −4 ,46
15 −0 ,66 65 −5 ,04
20 −1 ,01 70 −5 ,80
25 −1 ,37 75 −6 ,56
30 −1 ,72 80 −7 ,34
35 −2 ,06 85 −8 ,14
40 −2 ,41 90 −8 ,92
45 −2 ,85 95 −9 ,85
50 −3 ,38 98 −10, 41
a. From J. Jorgenson and D. R. Hartter, J. Am. Chem. Soc.,
85, 878 (1963).
Showing how sensitive is the strength on concentration for
such an acid (because it is influence also by ionic strength)

on wiki is widespread the value you reported (-3) and also
the R. Williams confirms this datum realative to diluted
aqueous solutions.

so i was misleaded by the data of concentrated systems
and/or poor gas phase proton affinity.
Diluted in water this acid is leveled (and equilibria
complicated by the not negligible concentration of SO4(2-))

> dodecyl sulfuric ester = lauryl sulfate = dodecyl sulfuric
> acid: −0,09*

uhm that -0,09 seems very strange ... it would be an acid
more than 40 times weak than H3O(+), weaker also than HNO3,
which sounds surprising ...

(it is known than in conc. sulfuric acid, nitric acid IS
PROTONATED and dehydrated to nitronium ion)

>
> *) Stahl, P. H.; Wermuth, C. G.: Handbook of Pharmaceutical
> Salts:
> Properties, Selection, and Use. 2002, Helvetica Chimica
> Acta, ISBN
> 3-906390-26-8
>
>
> That means: dodecyl sulfuric acid is a very strong acid, but
> a weaker acid than sulfuric acid.

is eventually a titration plot available ?

A non leveling solvent (such as glacial acetic acid or
acetic anhydride) would be the only reliable mean to obtain
data of relative strengths of these acids.
But i didn't look for such data yet ...