Making a Bromoalkane (1-bromopentane)
Summary
TLDRThis video delves into the synthesis of 1-bromo pentane, an alkyl halide, through a substitution reaction using sodium bromide, sulfuric acid, and pentanol. The process involves in situ preparation of hydrobromic acid, careful addition of reagents, and a reflux to ensure completion. The product, 1-bromo pentane, is separated via distillation and washing steps, resulting in a yield of about 60 grams with a 66 percent yield. The video also hints at future content, including the conversion of 1-bromo pentane into caproic acid, known for its strong, goat-like odor.
Takeaways
- π 1-Bromo pentane is an alkyl halide, a simple molecule where a hydrogen in pentane is replaced by bromine.
- π The position of the bromine atom is crucial and determines the compound's name, such as 1-bromo pentane, 2-bromo pentane, etc.
- π§ͺ Alkyl halides are versatile in organic chemistry, often used in substitution and Grignard reactions, as demonstrated in previous videos.
- π The choice of halogen (fluorine, chlorine, bromine, iodine) affects the physical properties and reactivity of the alkyl halide.
- π§ͺ The video demonstrates the synthesis of 1-bromo pentane, which will later be used to produce caproic acid, known for its strong, unpleasant odor.
- π The preparation requires sodium bromide, concentrated sulfuric acid, and pentanol, with specific quantities used for the reaction.
- βοΈ An ice bath is used to keep the reaction temperature low, preventing unwanted side reactions like bromine formation.
- π₯ The reaction involves in situ preparation of hydrobromic acid from sodium bromide and sulfuric acid, which then reacts with pentanol.
- π‘οΈ A reflux procedure is used to drive the reaction to completion, heating the mixture to its boiling point and condensing the vapors back into the flask.
- β±οΈ The reaction mechanism involves an SN2 substitution, where the hydroxyl group of pentanol is replaced by a bromine atom in a concerted step.
- π The final yield of 1-bromo pentane was approximately 60 grams, with a percent yield of about 66%, which is lower than expected but sufficient for further use.
Q & A
What is 1-bromo pentane and what class of molecules does it belong to?
-1-bromo pentane is a compound where one hydrogen atom in pentane (a simple alkane) is replaced by a bromine atom. It belongs to the class of molecules known as alkyl halides.
Why is the position of the bromine atom in 1-bromo pentane significant in its naming?
-The position of the bromine atom is significant because it affects the compound's properties and reactivity. The name '1-bromo pentane' specifically indicates that the bromine is attached to the first carbon in the pentane chain, distinguishing it from other possible isomers like '2-bromo pentane' or '3-bromo pentane'.
What are the common reactions that alkyl halides like 1-bromo pentane are used in?
-Alkyl halides are commonly used in substitution reactions and Grignard reactions in organic chemistry.
What is the significance of the choice of halogen in the synthesis of alkyl halides?
-The choice of halogen is important as it influences both the physical properties and the reactivity of the resulting alkyl halide. Different halogens can lead to different outcomes in reactions.
What is the purpose of making 1-bromo pentane in the described video?
-In the video, 1-bromo pentane is synthesized as an intermediate compound to eventually produce caproic acid, which is known for its strong, goat-like or animal-like scent.
What are the main reagents required for the preparation of 1-bromo pentane as described in the script?
-The main reagents required for the preparation of 1-bromo pentane are sodium bromide, concentrated sulfuric acid, and pentanol.
Why is the reaction mixture cooled on an ice bath during the addition of concentrated sulfuric acid?
-The reaction mixture is cooled on an ice bath to keep the temperature low during the addition of concentrated sulfuric acid, which releases a lot of heat. This helps prevent the formation of unwanted byproducts like bromine.
What does it mean to make a reagent 'in situ' and why is it done in this reaction?
-Making a reagent 'in situ' means preparing it within the reaction flask itself rather than pre-making it. In this reaction, hydrobromic acid is made 'in situ' by reacting sulfuric acid with sodium bromide, which is more time-efficient.
How is the 1-bromo pentane separated from the reaction mixture after the reaction is complete?
-After the reaction is complete, 1-bromo pentane is separated from the reaction mixture by carrying out a simple distillation, where the crude 1-bromo pentane is collected based on its boiling point.
What is the role of concentrated sulfuric acid in the washing steps after the initial distillation?
-Concentrated sulfuric acid is used in the washing steps to clean out and remove any side products or unreacted pentanol that might remain in the 1-bromo pentane.
How is the final yield of 1-bromo pentane determined and what was the yield percentage in the video?
-The final yield of 1-bromo pentane is determined by the amount of product collected after all purification steps. In the video, the yield was about 60 grams, which represents a percent yield of about 66 percent.
Outlines
π§ͺ Synthesis of 1-Bromo Pentane
The video script introduces the synthesis of 1-bromo pentane, an alkyl halide, by replacing a hydrogen atom in pentane with bromine. The process involves the preparation of hydrobromic acid in situ from sodium bromide and concentrated sulfuric acid. The reaction with pentanol (1-pentanol) is carried out under controlled temperature conditions to avoid side reactions and the formation of bromine. The video also discusses the importance of alkyl halides in organic chemistry, particularly in substitution and Grignard reactions. The final product, 1-bromo pentane, is intended for further conversion into caproic acid, known for its strong, unpleasant odor.
π¬ Distillation and Purification of 1-Bromo Pentane
After the initial reaction, the script describes the process of distillation to purify the crude 1-bromo pentane. The mixture is heated to boiling, and the vapors are condensed back into the flask to reflux the reaction mixture. This step facilitates the completion of the reaction and helps in obtaining a higher yield of 1-bromo pentane. The script explains the separation of the product from the reaction mixture by observing the layers formed after the reaction. The upper layer, containing the 1-bromo pentane, is separated from the lower aqueous layer. The process involves multiple washing steps with water and other reagents to remove impurities and byproducts, such as sulfuric acid and unreacted pentanol.
π Yield and Further Plans
The script concludes with the final yield of 1-bromo pentane, which is approximately 60 grams with a percent yield of about 66 percent. This yield is lower than the expected 80 to 90 percent, but it is sufficient for the subsequent synthesis of caproic acid. The video creator expresses gratitude to supporters on Patreon and mentions plans to enhance the Patreon page with more rewards and exclusive content. The script also provides a sneak peek into upcoming videos, including one on lithium peroxide, and invites viewers to share suggestions and ideas for future content.
Mindmap
Keywords
π‘Alkyl halides
π‘Pentane
π‘Substitution reactions
π‘Grignard reactions
π‘Halogens
π‘Caproic acid
π‘In situ preparation
π‘Reflux
π‘Distillation
π‘Fractional distillation
π‘Percent yield
Highlights
1-bromo pentane is an alkyl halide, structurally similar to pentane with a bromine atom replacing one hydrogen.
The position of the bromine atom is crucial, hence the specific naming like 1-bromo pentane.
Alkyl halides are versatile in organic chemistry, particularly in substitution and Grignard reactions.
The choice of halogen in alkyl halides affects both physical properties and reactivity.
1-bromo pentane is used to synthesize caproic acid, known for its strong, unpleasant odor.
The preparation requires sodium bromide, sulfuric acid, and pentanol, with specific quantities detailed.
Sodium bromide is added in portions to prevent stirring issues, with some undissolving being normal.
An ice bath is used to control the temperature during the addition of concentrated sulfuric acid.
In situ preparation of hydrobromic acid from sodium bromide and sulfuric acid is highlighted.
Pentanol is added slowly to the reaction mixture to ensure proper mixing and avoid hot spots.
A reflux process is used to drive the reaction to completion, with a timer set for two hours.
The substitution reaction mechanism involves protonation and nucleophilic attack by bromide ions.
Distillation is chosen over a separatory funnel for product separation, aiming for purity.
The boiling point of 1-bromo pentane is used to collect the product during distillation.
Washing steps with water and sulfuric acid are crucial for removing impurities from the product.
Saturated sodium bicarbonate solution is used in the final wash to ensure no residual acid remains.
Calcium chloride is used as a drying agent to remove water from the 1-bromo pentane.
Fractional distillation is performed to obtain a purer form of 1-bromo pentane.
The final yield and percent yield of 1-bromo pentane are calculated, with a discussion on yield factors.
The use of molecular sieves to keep the final product dry is mentioned, along with plans for future videos.
Transcripts
1-bromo pentane belongs to a class of
molecules known as alkyl halides and
it's structurally quite simple on the
left here we have pentane which is an
example of a simple alkane on the right
we have our one bromo pentane which is
very similar except one hydrogen has
been replaced with bromine it's
specifically called one bromo pentane
and not just bromo pentane so that we
know exactly where the bromine is on the
pentane molecule if we were to move the
bromine atom to a different carbon the
name could change to something like two
broma pentane or even three bromo
pentane in general alkyl halides are
very useful in organic chemistry and
they're used in a multitude of reactions
I would say that two of the most common
reactions that alkyl halides are used in
our substitutions and grignard reactions
i've carried out these types of
reactions a few times on my channel and
if you're interested I've provided some
links in the description in this video
we're making a bromo alkane but we can
also make alkyl halides using the other
halogens like fluorine chlorine or
iodine the choice of which halogen is
used is important because it will
influence both the physical properties
of the alkyl halide as well as its
reactivity in the end though there's
really no best halogen to use and it
really depends on what you're trying to
do the 1-bromo pentane that i make in
this video will be used to make
something called caproic acid as some of
you might know I'm a pretty big fan of
things that don't smell very good and
caproic acid is supposed to be pretty
repulsive in literature it's often said
to have a goat like or animal like scent
and I wanted to check it out for myself
for this preparation we need three main
things sodium bromide concentrated
sulfuric acid and one Penton all in
terms of quantities I use 78 grams of
sodium bromide 65 milliliters of one
Penton all and 60 milliliters of the
concentrated sulfuric acid to start
things off I added 75 milliliters of
distilled water to a 500 milliliter
round bottom flask with strong stirring
I added 78 grams of sodium bromide in
several small portions the sodium
bromide is added in small amounts
because if we were to add it all at once
it would jam up the stir bar not all of
the sodium bromide is going to dissolve
so it's normal if there's still a little
bit left at the bottom the sodium
bromide solution is then placed on an
ice bath and things are allowed to cool
above the flask I set up an addition
funnel and I slowly added 60 milliliters
of concentrated sulfuric acid the
addition of the sulfuric acid releases a
lot of heat and it's important to keep
the temperature as low as possible in
theory we don't absolutely need an ice
bath but if things get too hot we can
actually start to produce bromine which
we really don't want when the sulfuric
acid is added to the flask it reacts
with the sodium bromide to form sodium
bisulfate and hydrobromic acid
hydrobromic acid is the active reagent
that will react with the alcohol to make
the bromo alkane when a reagent is made
in the reaction flask itself instead of
being pre-made it's said to be made in
situ which can be roughly translated to
on site there are various different
reasons why in chemistry you'd want to
make a reagent and sit you but here it's
just much more time efficient because we
don't have to prepare hydrobromic acid
in advance when the sulfuric acid is
added it forms sodium sulfate which has
a lower solubility than sodium bromide
as we approach the end of the edition we
might have a lot of solid salt floating
around which might clump up and prevent
things from stirring to get things to
stir again the ice bath was removed and
things were allowed to warm up a little
bit
the next thing to add to the reaction
flask is the alcohol so - the same
addition funnel that we had our sulfuric
acid in I added 65 milliliters of one
Penton all with strong stirring the one
Penton all is added slowly and drop-wise
the addition of the alcohol will
generate some heat so we added slowly
and with strong stirring to make sure
that we don't generate any hot spots
it really doesn't generate that much
heat though so we can add it much
quicker than we added the sulfuric acid
by the end of the addition some of the
one Penton all has reacted to form one
bromo pentane but we still have a lot of
unreacted one Penton all left over to
push things forward and to get our
reaction to completion we need to heat
things up and the best way to do this is
to carry out a reflux the contents of
the reaction flask are heated to the
boiling point and the vapors that come
off are rhe condensed back into the
flask this allows us to heat the
reaction to the boiling point of the
mixture with very little loss to get
things started
we get some strong stirring going and I
turn on the heating mantle initially the
solution was opaque due to undissolved
salts but as it heats up the salts
dissolve into solution and it becomes
clear once the contents of the flask are
boiling and we have liquid Rican denting
we start our timer and we let the reflux
go for about two hours the type of
reaction that we're carrying out is
generally known as a substitution
reaction I've covered substitution
reactions though in previous videos so I
don't really want to get into too many
details here for those of you who are
interested in knowing more though I'll
provide a link in the description to a
more detailed video the overall reaction
is shown here where the hydroxyl group
of the one Penton all is being converted
to a bromine the conversion from the
alcohol to the bromo alkane is
facilitated by the hydrobromic acid that
we made in sit you now I'm just going to
quickly
go over the mechanism in the first step
the hydroxyl group of one Penton all is
protonated to form a water molecule the
water molecule that's formed is quite
stable on its own and it's pretty much
just looking for an excuse to leave in
one concerted step a bromide ion from
hydrobromic acid attacks and the water
molecule pops off in organic chemistry
there are many types of substitution
reactions but this one is specifically
known as sn2 after two hours the reflux
is complete so I take away the heating
mantle and I let things cool down a
little bit when we take a look at the
flask from the side we can see that we
have two layers where the upper layer is
our one bromo pentane to separate the
one bromo pentane from the reaction
mixture we're going to carry out a
simple distillation instead of using
simple distillation to separate the
crude one bromo pentane I could have
also used the separatory funnel both
methods are equally as viable but I
think the distillation gives a slightly
cleaner product in the end though it
doesn't really matter because the one
bromo pentane we get from both methods
is crude and we have two redistill it
anyway the literature boiling point of
one bromo pentane is 130c so we collect
everything that comes over below this
below 130 C we should be collecting
three main things water azeotropic
hydrobromic acid and our product one
bromo pentane in the reaction flask will
leave behind sulfuric acid unreacted one
Penton all and salt side products when I
look at the receiving flask at the end I
can see that we have two layers and
honestly at this point I don't know
exactly which one our product is the
density of the aqueous layer is pretty
much determined by how much hydrobromic
acid is present and I have no way of
knowing this if there's very little
hydrobromic acid present the one bromo
pentane has a higher density and it
should be on the bottom but if there's a
lot of hydrobromic acid present then the
one bromo pentane is going to be sitting
on top this really isn't a problem
though and when I do the workup I'll
show you how I determine which layer is
which when we take a look at the
reaction flask we're left with a nice
syrupy mix
year of sulfuric acid and salts as long
as it's hot it remains a liquid but as
it cools down it solidifies this really
isn't a huge problem though and the
salts are pretty easily washed out with
water the contents of our receiving
flask is then transferred to a
separatory funnel once everything's in
the separatory funnel we still don't
know which layer is which but we'll find
out after I dilute things with a little
bit of water I had a whole bunch of
water to the separatory funnel and this
serves to dilute the aqueous layer and
lower its density by adding something
like a hundred milliliters we pretty
much guarantee that the aqueous layer
will have a lower density than the
1-bromo pentane the separatory funnel is
taken off the stand and I shake it to
mix things up every so often we pause
and open the stopcock to release any
pressure that might have built up after
the layers have settled our 1-bromo
pentane should be at the bottom and this
is drained off into an Erlenmeyer flask
the upper aqueous layer in the
separatory funnel is waste and it can be
disposed of we are done with our washing
steps though and the 1-bromo pentane is
poured back into the separatory funnel
to the separatory funnel i then pour in
25 milliliters of concentrated sulfuric
acid we add the sulfuric acid here
because it's good at cleaning out and
getting rid of any side products or one
Penton all that might remain just like
before we take our separatory funnel off
the stand and we mix things up it's
important to be especially careful in
these steps though because we are
working with concentrated sulfuric acid
after things are mixed up the funnel is
placed back on the stand the layers are
allowed to separate and we drain off the
lower sulfuric acid layer
our 1-bromo pentane is much cleaner but
now it's full of sulfuric acid so we
need to wash it with a little bit of
water the addition of the sulfuric acid
gave us a yellow color but when we shake
things up with water it goes back to
being white the solution is placed back
on the stand the layers are allowed to
separate and again our lower one bromo
pentane layers drained off the one bromo
pentane is then returned to the
separatory funnel for one last washing
this final washing is to just make sure
that there's no acid that might remain
and to do this we use a hundred
milliliters of saturated sodium
bicarbonate solution just like all the
other washings we mix things thoroughly
we let the layers separate and then we
drain off the lower one bromo pentane
the cloudiness of the one bromo pentane
is due to the presence of water so we're
going to need to dry things up a little
bit using a drying agent I chose to use
calcium chloride as my drying agent so I
just dumped a bunch in swirled it around
and let it stand for a while the calcium
chloride dries the 1-bromo pentane by
forming a complex with the water the
flask was Stoppard and i left for an
hour and when I came back we can see
that the solution is much clearer the
one bromo pentane is separated from the
calcium chloride by just filtering it
through a little bit of cotton i
filtered things directly into a round
bottom flask because the next step is to
carry out a distillation after
everything it filtered through I set
things up for a fractional distillation
to get the distillation started I turn
on the heating mantle and I cover the
fractional column with some aluminum
foil just after several minutes things
will come to a boil and the vapor will
start to travel up the column eventually
the vapor made it to the top of the
column and finally to the condenser and
we start to collect things at around 70
C the first step that came over here was
slightly yellow and the boiling point of
our one bromo pentane is 130 so this
clearly isn't our product
at around 125 C our receiving flask was
swapped out for a new one the rate of
the distillation picked up and the bulk
of the 1-bromo pentane came over between
125 and 130 C the distillation was
stopped when there was very little
liquid left over in the distillation
flask the apparatus was dismantled and
when we take a look at our receiving
flask we see we have quite a bit of
product the 1-bromo pentane that we
collected here came over between 125 and
130 C and this is a pretty broad boiling
range for me this is pure enough but if
a higher purity was needed I would have
had to distill it probably a few more
times I actually already made one bromo
pentane in a previous video using
phosphorous tribromide and I figured I
would just combine everything
at the bottom of the bottle we have
molecular sieves to keep things dry but
they're pretty old so I decided to add
some new ones
after the sieve I pour it in the 1-bromo
pentane that we got from this video
the final yield of one bromo pentane was
about 60 grams which represents a
percent yield of about 66 percent the
normal yields for this reaction are
between 80 and 90 percent so what I got
here is quite low I'm honestly not sure
why the yield is so much lower than it
should be anyway I have more than enough
to make my caproic acid and that video
should be posted eventually I think I'll
post the lithium peroxide video next
because that is been sitting on the
shelf for a while
anyway as usual I'd like to extend a big
thanks to all of my supporters on
patreon and especially those who donate
five dollars or more
anyone who donates and supports man
patreon gets to see my videos 24 hours
before I release it to YouTube and if
you donate five dollars or more you get
your name at the end of the video like
you see here in the next few months
though I want to work on my patreon page
a lot and I want to get more rewards
going and maybe even get some higher
tier ones and I want to also offer some
patreon exclusive content also as usual
here's the videos that I've currently
filmed and the ones I plan to work on if
you have any suggestions or ideas please
feel free to leave them in the comments
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