Inorganic compounds flammable when wet

Most of the discarded flammable inorganic compounds when wetted have been stored for a long time, poorly stored, and caused air leakage and moisture absorption after opening and use, or the tightness of the packaging has been destroyed.

1.

Take LiBH4 ( lithium borohydride ) as an example

For acid quenching, LiBH ₄ first decomposes to generate borane , and then decomposes into hydrogen, which manifests as a large amount of gas overflowing the liquid surface.

The excess LiBH4 in the quenching synthesis reaction can also be adjusted with an acidic aqueous solution until no bubbles are formed.

Note: ① Good ventilation is required to dilute and exhaust the flammable gas produced in time

2.

Lithium aluminum tetrahydrogen is also called aluminum lithium hydrogen, lithium aluminum hydride or LAH.

Dissolving or suspending the waste lithium aluminum tetrahydrofuran in anhydrous tetrahydrofuran, because the volatilized gas of tetrahydrofuran and the oxygen generated from the water in the tetrahydrofuran can make a certain area above the liquid form a combustion limit or an explosion limit.

LiAIH4 _.

LiAlH ₄ +4H ₂ O=Al(OH) ₃ +LiOH+4H ₂ ↑

Items stained with trace amounts of tetrahydroaluminum lithium, such as weighing paper, straw paper, horn spoons, packaging bottles, and empty plastic bags, must be thoroughly quenched together to ensure safety

Lithium aluminum tetrahydrogen is a very important chemical reducing reagent in organic synthesis.

So, how much water is the most appropriate to quench the excess lithium aluminum tetrahydrogen in the reaction? Taking the reaction of reducing ester with lithium tetrahydrogen aluminum as an example, the following two reaction formulas should be combined to calculate

First calculate the reduction of the substrate esters and see how much water is needed:

4R'CO ₂ R-3LiAlH ₄ +6H ₂ O=4R'CH ₂ OH+3LiAlO ₂ +4ROH+4H ₂ ↑

Look at how much water is needed for the remaining tetrahydroaluminum lithium:

LiAlH ₄ +2H ₂ O=LiAlO ₂ +4H ₂ ↑

Combining the above two, we can know: How many moles of tetrahydroaluminum lithium are put in, add twice the number of moles of tetrahydroaluminum lithium, and the aim is: the amount of water should be such that the tetrahydroaluminum lithium exactly generates granular lithium metaaluminate.

For neutral or acidic products, the LiOH and A1(OH) ₃ produced can be dissolved and extracted by adding acid or a saturated NH ₄ C1 solution during post-treatment .

According to the requirements of the reaction product for acid and alkali, determine the pH of the quenching aqueous solution, and the more important thing is to calculate the exact quenching water consumption, no more or no less

3.
Sodium, potassium, lithium

When preparing sodium alkoxide, the small block of sodium can be directly dissolved in alcohol
.
A more reliable and safe way to quench waste sodium lumps, sodium skins or sodium scraps is to suspend sodium in dry tetrahydrofuran , slowly add alcohol under stirring until all is dissolved, and then neutralize with dilute acid
.

Lithium, sodium and potassium are all chemically active alkali metals.
By comparing the reaction with alcohols, their chemical activity order is: lithium<sodium<potassium, so after suspending them in dry tetrahydrofuran, lithium can be used with methanol For quenching, sodium is quenched with ethanol , and potassium is quenched with isopropanol or ethanol
.

In order to prevent the generated hydrogen from catching fire, it is best to carry out under the condition of continuous diluting with nitrogen flow, especially when quenching metallic potassium
.
Metal sodium or potassium reacts with high concentrations of halides and tends to explode
.

4.
NaH, KH, LiH, CaH ₂

Sodium hydride (NaH) is also called sodium hydrogen.
Because it is too active and flammable, it must be dispersed in mineral oil to reduce the risk of combustion.
The mass fraction is generally below 60%
.
It can be directly put into the reaction.
If you need to remove the oil, you can wash it with n-hexane, and then pour out the n-hexane.
Be sure to avoid pouring dry, otherwise it is very dangerous and easy to catch fire suddenly
.
Under normal circumstances, there is no need to clean too many times, unless mineral oil affects the reaction
.
For example, if the system is viscous and there is oil and then bubbles are generated, it is easy to flush
.
Quench the waste NaH by suspending it in dry tetrahydrofuran, and slowly add ethanol or isopropanol under stirring until hydrogen is no longer released and clarified.
The inner wall of empty plastic bags or packaging bottles often has a small amount of NaH adhered to it.
Regardless of whether it is present or not, it must be rinsed with ethanol before the danger is eliminated
.
If you don't do this, just throw it into the trash can.
Sparks will ignite other objects
.
The excess NaH after the quenching reaction can be quenched by directly adding water or alcohol dropwise slowly
.

The treatment methods of KH and LiH are the same as those of NaH
.
The chemical activity of CaH ₂ is much lower than that of NaH, and it is mainly used to prepare various anhydrous organic solvents in the laboratory
.
The waste CaH, or the CaH after preparing anhydrous solvent, can be directly diluted with absolute ethanol, and then gradually added to an open container with a large amount of water in batches.
A large amount of hydrogen will be released, but the heat will not be released.
Obviously
.

5.
Alkali metal amines

Alkali metal amides are a class of strong deprotonated bases, including lithium amide, sodium amide, potassium amide and so on
.

Sodium amide will explode when exposed to water, and it has also exploded when taking out the long-stored sodium amide from the container
.

To quench the waste alkali metal amines, dissolve them in dry toluene or tetrahydrofuran, slowly add alcohol or water under stirring, and finally neutralize with dilute hydrochloric acid.
The empty packaging bottles should also be quenched thoroughly
.
After quenching the reaction, the excess alkali metal amine can be directly and slowly added dropwise with alcohol or water for quenching
.

6.
Boranes

Borane, also known as borohydride compound, is a general term for compounds composed of boron and hydrogen, or boron and alkyl
.
Borane (BH) is only found in gas and cannot exist alone.
The simplest borane is diborane (B ₂ H ₆ )
.
Commonly used are the large hindered 9-borane bicyclo[3,3,1]nonane (abbreviated as 9-BBN), chiral reducing agent (-) diisopine pinyl chloroborane [abbreviated as (-)- DIPC1] and so on
.

Borane can undergo hydrolysis, halogenation, amination, hydrogenation, alkylation, alcoholysis and other reactions, and can also react with metal organic compounds
.
According to statistics, most of them are used for reduction reactions in chemical laboratories
.

Borane has an unpleasant odor.
The chemical properties of low-grade borane (with a small number of boron atoms) are very active.
When high-concentration borane is in contact with air, it will decompose explosively, so it must be dissolved in ethers and other stability.
In the liquid, a solution with a lower concentration such as 0.
5mol/L or 1.
0mol/L is made, which is easy to use and relatively safe
.

Commercially available borane is generally dissolved in THF or dimethyl sulfide to form a complex, such as borane tetrahydrofuran complex, borane dimethyl sulfide complex, borane pyridine complex, triphenyl Borane complex, catechol borane, 2-picoline borane, NN-diethyl aniline borane, triethyl boron, diethyl (3-pyridyl) borane, triethyl Lithium borohydride and so on
.
More than two dozen boranes are used in the laboratory
.

Borane will burn when exposed to air, or even flash and explode.
The reaction formula is

B ₂ H ₆ +3O ₂ =B ₂ O ₃ +3H ₂ O

Borane will burn when exposed to water, release a lot of heat or even explode, the reaction formula is

B ₂ H ₃ +6H ₂ O=2B(OH) ₃ ↓+6H ₂ ↑

To quench the waste borane reagent, you can first dissolve it in 10 times the volume of anhydrous THF under the protection of nitrogen (if it is general THF, do a small test first to avoid overflow or fire accidents due to high moisture content) , And then add methanol or ethanol dropwise until no bubbles are generated
.

After the reaction involving borane is completed, it is generally quenched with methanol and other alcohols, first in an ice bath (dry ice bath is not allowed, the temperature is too low to react, it is terrible to accumulate the potential and then erupt!), add methanol drop by drop .
Especially at the beginning, it must be very slow, because a large number of bubbles are formed, and it is easy to overflow the reaction liquid and cause accidents
.
Nitrogen can be added for blowing, but ventilation and protective measures should also be paid attention to
.
When you start quenching, you must be patient, and you can't ask for it quickly.
Unlike lithium aluminum hydride and sodium hydride, it is quenched quickly.
Borane requires a longer process to quench completely
.
When excessive methanol is added, the solution can be heated up slightly and reflux slowly, and it usually takes more than half an hour to quench the solution
.

For other borane complexes and 9-BBN quenching methods, please refer to alkanes
.