Sciencemadness Discussion Board

Preparation/Exploration of Mg(ClO)2.2Mg(OH)2, a Solid Hypochlorite

AJKOER - 16-10-2013 at 14:19

For those with limited access to Calcium hypochlorite, here is an easy path to a solid hypochlorite, so called Dibasic magnesium hypochlorite (abbreviated as DBMH as its chemical formula Mg(ClO)2.2Mg(OH)2.xH2O isn't exactly shorthand). Here is a relatively recent patent (1992) that generally cites the method I employed. To quote (link http://ip.com/patfam/en/16863755):
:

"Abstract (English, JP 04108602 A) PURPOSE: To obtain basic magnesium hypochlorite useful for a germicide with high fixing rate of effective chlorine in a short time by adding alkali metal hydroxide to an aq. mixture soln. of inorg. compd. having a hypochlorous acid group and magnesium salt. CONSTITUTION: An inorg. compd. having a hypochlorous acid group (e.g. sodium hypochlorite) and a magnesium salt (e.g. magnesium chloride) are added to water and mixed. Then, an alkali metal hydroxide (e.g. sodium hydroxide) is added to this aq. mixture soln. to cause reaction. The precipitated basic magnesium hypochlorite is separated by filtering, washed with water and dried to obtain the basic magnesium hypochlorite. The proper proportion of each source material used is 1.4-2.3mol of magnesium salt and 2-3.5mol of alkali metal hydroxide to 1mol of hypochlorous group. COPYRIGHT: (C)1992,JPO&Japio"

My take on the net reaction equation (see derivation below) where I somewhat differently (based on my analysis) add the dry Magnesium sulfate hydrate (Epsom salt) to a extra strength Sodium hypochlorite solution (8.25%) to which NaOH has been added:

3 MgSO4 + [ NaClO + 2 NaOH ] --> 3 Na2SO4 + Mg(ClO)2.2Mg(OH)2 (s)

Or, per mole of hypochlorite:

1.5 MgSO4 + [ NaClO + 2 NaOH ] --> 1.5 Na2SO4 + 1/2 Mg(ClO)2.2Mg(OH)2 (s)

I would recommend that one waits for the reaction to move to completion over some hours as I have witness the relative concentration of the white DBMH suspensions apparently does gradually increases with time (which would be consistent with my reaction cycling scenario outlined below).

The product is an annoying fine white suspension (see patent at http://www.google.com/patents?hl=en&lr=&vid=USPAT412... where a nominal particle size is quoted at 160 microns) with a strong chlorine smell. Apparently, per the same reference, the DBMH is insoluble when the pH is 10.5 or higher.
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Observed properties so far.

1. Difficult to filter.
2. Reacts with NaHSO4 to form Cl2.
3. Reacts with H2O2 to form O2.
4. Reacts with vinegar to also produce a chlorine odor.
5. Does not react violently with aqueous ammonia, but the resulting salt appears to be a chlorate (heating on a dried sample on Aluminum foil produced a reaction consistent with a strong oxidizer).

The latter suggests the general instability of the DBMH disproportionating into chloride and chlorate. Reference see page 669 at http://books.google.com/books?id=FnrTAAAAMAAJ&pg=PA669&a... to quote:

"Now chlorine was passed into a milk of- magnesium hydroxide and water, at temperatures between o° and 100°. Even at 0°, together with magnesium hypochlorite, much chlorate was formed, more than corresponding to half of the chlorine entering into the reaction. At 15° a little more chlorate was formed, together with much hypochlorate, some of which was changed into chloride, with evolution of oxygen. In both solutions the hypochlorite is easily converted into chlorate, not merely by heating to 50°, but even by prolonged agitation by a current of air at ordinary temperatures. At 70° C, from the first mostly chlorate was formed, with a little chloride, produced by loss of oxygen. Hence magnesium hypochlorite in statu noscendi does not possess much stability and is easily transformed into chlorate."

I would invite others to experiment and report results with appropriate precautions.
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Derivation of Net Reaction Equation for DBMH:
Assume one starts by combining the reactant as follows:
3 MgSO4 + 6 NaClO ---> 3 Na2SO4 + 3 Mg(ClO)2
4 NaOH + 2 Mg(ClO)2 --> 2 Mg(OH)2 + 4 NaClO
Mg(ClO)2 + 2 Mg(OH)2 --> Mg(ClO)2 .2Mg(OH)2 (s)

So the net reaction is:
3 MgSO4 + 6 NaClO + 4 NaOH ---> 3 Na2SO4 + 4 NaClO + Mg(ClO)2 .2Mg(OH)2 (s)

However, given the leftover Sodium hypochlorite on the left one could possibly add more MgSO4 and NaOH to produce yet more DBMH as follows:

2 MgSO4 + 4 NaClO ---> 2 Na2SO4 + 2 Mg(ClO)2
8/3 NaOH + 4/3 Mg(ClO)2 --> 4/3 Mg(OH)2 + 8/3 NaClO
2/3 Mg(ClO)2 + 4/3 Mg(OH)2 --> 2/3 Mg(ClO)2 .2Mg(OH)2 (s)

or for a net addition:
2 MgSO4 + 4 NaClO + 8/3 NaOH --> 2 Na2SO4 + 8/3 NaClO + 2/3 Mg(ClO)2 .2Mg(OH)2 (s)

Similarly, the next net addition would be:

4/3 MgSO4 + 8/3 NaClO + 16/9 NaOH --> 4/3 Na2SO4 + 16/9 NaClO + 4/9 Mg(ClO)2 .2Mg(OH)2

Now, as the geometric series:
S = 1 + r + r2 + r3 + ...
rS = r + r2 + r3 + ..

sums to 1/(1-r) and given r is apparently 2/3 here, the series sum implies a multiplier of 1/(1-2/3) = 3.

So, the ultimate net equation is:
9 MgSO4 + [6 NaClO + 12 NaOH] ---> 9 Na2SO4 + 3 Mg(ClO)2.2Mg(OH)2 (s)

or, upon scaling:

1.5 MgSO4 + [ NaClO + 2 NaOH ] --> 1.5 Na2SO4 + 1/2 Mg(ClO)2 .2Mg(OH)2 (s)

as I stated above.


[Edited on 16-10-2013 by AJKOER]

blogfast25 - 17-10-2013 at 05:00

Quote: Originally posted by AJKOER  

Derivation of Net Reaction Equation for DBMH:
Assume one starts by combining the reactant as follows:
3 MgSO4 + 6 NaClO ---> 3 Na2SO4 + 3 Mg(ClO)2
4 NaOH + 2 Mg(ClO)2 --> 2 Mg(OH)2 + 4 NaClO
Mg(ClO)2 + 2 Mg(OH)2 --> Mg(ClO)2 .2Mg(OH)2 (s)

So the net reaction is:
3 MgSO4 + 6 NaClO + 4 NaOH ---> 3 Na2SO4 + 4 NaClO + Mg(ClO)2 .2Mg(OH)2 (s)



Huh?

No, the net reaction would be:

3 MgSO4 + 2 NaClO + 4 NaOH ---> 3 Na2SO4 + Mg(ClO)2 .2Mg(OH)2 (s)

Do you have any empirical evidence at all that your product corresponds to Mg(ClO)2 .2Mg(OH)2, in terms of elemental composition? At a minimum, dissolve the product and destroy all hypochlorite and determine Mg content (EDTA titration, for instance). Determination of Cl content isn't too hard either (AgCl route).



[Edited on 17-10-2013 by blogfast25]

AJKOER - 17-10-2013 at 14:55

OK, thanks for reviewing my work as I now see a typo. My suggested reaction per mole of NaClO is correctly presented as:

1.5 MgSO4 + [ NaClO + 2 NaOH ] --> 1.5 Na2SO4 + 1/2 Mg(ClO)2.2Mg(OH)2 (s)

or, on scaling to whole numbers, is:

3 MgSO4 + 2[ NaClO + 2 NaOH ] --> 3 Na2SO4 + Mg(ClO)2.2Mg(OH)2 (s)

which is, of course, your comment:

3 MgSO4 + 2 NaClO + 4 NaOH ---> 3 Na2SO4 + Mg(ClO)2 .2Mg(OH)2 (s)

indicating that no complex derivation is/was required.

On your question " Do you have any empirical evidence at all that your product corresponds to Mg(ClO)2 .2Mg(OH)2, in terms of elemental composition? ", actually this is not my product as I am just replicating the patent on a well known bleaching product.

Now, similar to the basic magnesium carbonate (formula: MgCO3.Mg(OH)2 ), there may be another compound with a similar formulation. See, for example (link: http://www.google.lt/patents/US4123377?hl=lt ) to quote:

"A basic magnesium hypochlorite was reported by Nozaki et al. in a Japanese publication abstracted in Chemical Abstracts, 48, 1413F (1954). The compound was attributed the formula

Mg(OH) (OCl.Mg(OH).sub.2).2H.sub.2 O"

which I would describe as a dibasic magnesium hydroxyhypochlorite dihydrate.

So to a given weight of the reputed DBMH, adding H2O2 one may be able to verify the amount of liberated O2 confirming, in part, the formula via the reaction:

Mg(ClO)2 + 2 H2O2 --> MgCl2 + 2 H2O + 2 O2 (g)

There is a potential complication as the actual formula for one or both of the basic magnesium hypochlorites may actually include a "2 H2O" term, or some other amount of water, distorting the correct molecular weight.

What I also find curious is that my chief source of information on properties and preparation for DBMH are associated with patents as there isn't much academic literature on it. I find this strange because this is a long known product with commercial applications. However, I am not complaining much on the relative obscurity, as there has been some misuses of the related Calcium based bleaching powder contributing to its notoriety.


[Edited on 18-10-2013 by AJKOER]

blogfast25 - 18-10-2013 at 04:29

Quote: Originally posted by AJKOER  

On your question " Do you have any empirical evidence at all that your product corresponds to Mg(ClO)2 .2Mg(OH)2, in terms of elemental composition? ", actually this is not my product as I am just replicating the patent on a well known bleaching product.



It's not your patent but when you replicate it experimentally it is your product. Just a basic determination of Mg and Cl would confirm (or not) that what you obtained is what is stated in the patent. This is not a priori so. Also the patent may be faulty. Plenty of those around...

symboom - 30-4-2018 at 15:17

Would magnesium hypochlorite be made from sodium chlorocyanurate TCCA and magnesium hydroxide

Or does this decompose

[Edited on 30-4-2018 by symboom]

AJKOER - 30-4-2018 at 20:31

Sodium chlorocyanurate and water forms HOCl (see https://www.unicef.org/cholera/Annexes/Supporting_Resources/... and also http://www.who.int/water_sanitation_health/dwq/chemicals/sod... ).

Then, with Mg(OH)2:

Mg(OH)2 + 2 HOCl --> Mg(OCl)2 + 2 H2O

And, with an excess of Mg(OH)2 possibly Mg(ClO)2.2Mg(OH)2, however, with a sodium salt hanging around the solution, I would not be too surprised if someone experimenting with aqueous sodium chlorocyanurate and Mg(OH)2 reported some double salt formation containing Na.

[Edited on 1-5-2018 by AJKOER]