Making a Bromoalkane (1-bromopentane)

Summary

This 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

• 🌟 1-Bromo pentane is an alkyl halide, a simple molecule where a hydrogen in pentane is replaced by bromine.
• 🔍 The position of the bromine atom is crucial and determines the compound's name, such as 1-bromo pentane, 2-bromo pentane, etc.
• 🧪 Alkyl halides are versatile in organic chemistry, often used in substitution and Grignard reactions, as demonstrated in previous videos.
• 🌐 The choice of halogen (fluorine, chlorine, bromine, iodine) affects the physical properties and reactivity of the alkyl halide.
• 🧪 The video demonstrates the synthesis of 1-bromo pentane, which will later be used to produce caproic acid, known for its strong, unpleasant odor.
• 📝 The preparation requires sodium bromide, concentrated sulfuric acid, and pentanol, with specific quantities used for the reaction.
• ❄️ An ice bath is used to keep the reaction temperature low, preventing unwanted side reactions like bromine formation.
• 🔥 The reaction involves in situ preparation of hydrobromic acid from sodium bromide and sulfuric acid, which then reacts with pentanol.
• 🌡️ 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.
• ⏱️ The reaction mechanism involves an SN2 substitution, where the hydroxyl group of pentanol is replaced by a bromine atom in a concerted step.
• 📉 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

00:00

🧪 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.

05:02

🔬 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.

10:03

📈 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.

Keywords

💡Alkyl halides

Alkyl halides are a class of organic compounds where a hydrogen atom in an alkane is replaced by a halogen. In the video, 1-bromo pentane is an example of an alkyl halide, specifically where a hydrogen in pentane is replaced by bromine. This substitution is crucial for the chemical reactions discussed in the video, as alkyl halides are versatile intermediates in organic synthesis.

💡Pentane

Pentane is a simple alkane, a hydrocarbon with the formula C5H12. It serves as the base molecule in the video, to which a bromine atom is added to create 1-bromo pentane. Pentane is used to illustrate the structural simplicity of alkanes and to contrast with the more complex alkyl halides.

💡Substitution reactions

Substitution reactions are a type of chemical reaction where an atom or group of atoms in a molecule is replaced by another atom or group. In the context of the video, the substitution reaction involves replacing a hydroxyl group in 1-pentanol with a bromine atom to form 1-bromo pentane, facilitated by hydrobromic acid.

💡Grignard reactions

Grignard reactions are a class of organic reactions that involve the use of Grignard reagents, which are organomagnesium compounds. Although not the main focus of the video, the script mentions that alkyl halides like 1-bromo pentane are commonly used in Grignard reactions, highlighting their utility in organic chemistry.

💡Halogens

Halogens are a group of non-metal elements in the periodic table, including fluorine, chlorine, bromine, iodine, and astatine. The video discusses the use of different halogens in the formation of alkyl halides, emphasizing how the choice of halogen can affect the physical properties and reactivity of the resulting compound.

💡Caproic acid

Caproic acid is a carboxylic acid with a six-carbon chain, and it is mentioned as the end product that the 1-bromo pentane will be used to synthesize. The video creator expresses interest in its distinctive, repulsive odor, which is described as goat-like or animal-like, adding a personal and sensory dimension to the chemical discussion.

💡In situ preparation

In situ preparation refers to the synthesis of a reagent directly in the reaction flask, as needed, rather than preparing it beforehand. In the video, hydrobromic acid is prepared in situ by reacting sodium bromide with sulfuric acid, which is highlighted as a time-efficient method in the context of the chemical procedure being demonstrated.

💡Reflux

Reflux is a technique used in chemistry to apply heat to a reaction mixture by boiling the solvent and then condensing the vapors back into the reaction flask. This allows the reaction to proceed at the boiling point of the mixture without loss of solvent. In the video, reflux is used to drive the substitution reaction to completion by heating the mixture containing 1-pentanol and hydrobromic acid.

💡Distillation

Distillation is a separation technique that exploits the differences in volatilities of components in a boiling liquid mixture. The video describes a simple distillation process to separate 1-bromo pentane from the reaction mixture based on differences in boiling points, which is a common practice in organic chemistry for purifying compounds.

💡Fractional distillation

Fractional distillation is a more refined distillation process that separates components of a mixture based on their different boiling points. It is used in the video to purify the crude 1-bromo pentane obtained from the initial distillation, with the aim of obtaining a product with a narrower boiling range, indicating higher purity.

💡Percent yield

Percent yield is a measure of the actual amount of product obtained from a chemical reaction compared to the theoretical amount that could be produced. The video concludes with a discussion of the percent yield of 1-bromo pentane, which was lower than expected, prompting the creator to consider possible reasons for the discrepancy.

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

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thanks to all of my supporters on

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tier ones and I want to also offer some

patreon exclusive content also as usual

here's the videos that I've currently

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